internal/fwserver: Ensure Attribute and Block plan modification returns custom value type implementations

[bflad]

Closes #754
Reference: #715 (precursor)
Reference: #767 (followup)

The framework recently was updated to perform stricter value type checking against the defined schema type when setting data. This was to prevent panics or other potentially confusing behaviors with mismatched types. The attribute-based plan modification logic in the framework however was missing some value type conversion, which could generate unavoidable Value Conversion Error diagnostics for provider developers when attributes/blocks used both CustomType and PlanModifiers fields.

This changeset ensures that attribute-based plan modification will always return the custom value type implementation of a value after a plan modifier response. All plan modifier responses are currently using the base value type, so the framework logic must handle converting it back. Even if the plan modifier responses were updated to use the Valuable interfaces, the framework would still need to perform this logic in case a plan modifier implementation opted to return the base value type, since all base value types implement the Valuable interfaces currently.

These changes handle custom types on all attribute and block implementations, however a non-trivial amount of internal code refactoring is necessary to fix this same issue for NestedAttributeObject and NestedBlockObject implementations that contain both CustomType and PlanModifiers fields. That effort will follow this one separately to reduce review burden.

Previously before logic updates:

--- FAIL: TestServerPlanResourceChange (0.00s)
    --- FAIL: TestServerPlanResourceChange/create-attributeplanmodifier-response-attributeplan-custom-type (0.00s)
        /Users/bflad/src/github.com/hashicorp/terraform-plugin-framework/internal/fwserver/server_planresourcechange_test.go:3848: unexpected difference:   &fwserver.PlanResourceChangeResponse{
            - 	Diagnostics: diag.Diagnostics{
            - 		diag.withPath{
            - 			Diagnostic: diag.ErrorDiagnostic{detail: "An unexpected error was encounte"..., summary: "Value Conversion Error"},
            - 			path:       s"test_computed",
            - 		},
            - 	},
            + 	Diagnostics:    nil,
              	PlannedPrivate: &{Provider: &{data: {}}},
              	PlannedState: &tfsdk.State{
            - 		Raw:    s`tftypes.Object["test_computed":tftypes.String, "test_other_computed":tftypes.String, "test_required":tftypes.String]<"test_computed":tftypes.String<unknown>, "test_other_computed":tftypes.String<unknown>, "test_required":tftypes.String<"test-config-value">>`,
            + 		Raw:    s`tftypes.Object["test_computed":tftypes.String, "test_other_computed":tftypes.String, "test_required":tftypes.String]<"test_computed":tftypes.String<"test-attributeplanmodifier-value">, "test_other_computed":tftypes.String<unknown>, "test_required":tftypes.`...,
              		Schema: schema.Schema{Attributes: {"test_computed": schema.StringAttribute{CustomType: s"StringTypeWithSemanticEquals(false)", Computed: true, PlanModifiers: {...}}, "test_other_computed": schema.StringAttribute{Computed: true}, "test_required": schema.StringAttribute{Required: true}}},
              	},
              	RequiresReplace: s"[]",
              }

--- FAIL: TestAttributePlanModifyString (0.00s)
    --- FAIL: TestAttributePlanModifyString/response-planvalue-custom-type (0.00s)
        /Users/bflad/src/github.com/hashicorp/terraform-plugin-framework/internal/fwserver/attribute_plan_modification_test.go:8315: unexpected difference:   &fwserver.ModifyAttributePlanResponse{
            - 	AttributePlan:   basetypes.StringValue{state: 2, value: "testvalue"},
            + 	AttributePlan:   types.StringValueWithSemanticEquals{StringValue: basetypes.StringValue{state: 2, value: "testvalue"}},
              	Diagnostics:     nil,
              	RequiresReplace: s"[]",
              	Private:         nil,
              }

--- FAIL: TestAttributeModifyPlan (0.00s)
    --- FAIL: TestAttributeModifyPlan/attribute-list-nested-usestateforunknown-custom-type (0.00s)
        /Users/bflad/src/github.com/hashicorp/terraform-plugin-framework/internal/fwserver/attribute_plan_modification_test.go:1733: Unexpected response (-wanted, +got):   fwserver.ModifyAttributePlanResponse{
            - 	AttributePlan: types.ListValueWithSemanticEquals{
            - 		ListValue: basetypes.ListValue{
            - 			elements: []attr.Value{
            - 				basetypes.ObjectValue{
            - 					attributes:     map[string]attr.Value{...},
            - 					attributeTypes: map[string]attr.Type{...},
            - 					state:          2,
            - 				},
            - 			},
            - 			elementType: basetypes.ObjectType{AttrTypes: map[string]attr.Type{"nested_computed": basetypes.StringType{}}},
            - 			state:       2,
            - 		},
            - 	},
            + 	AttributePlan: basetypes.ListValue{
            + 		elements: []attr.Value{
            + 			basetypes.ObjectValue{
            + 				attributes:     map[string]attr.Value{"nested_computed": basetypes.StringValue{...}},
            + 				attributeTypes: map[string]attr.Type{"nested_computed": basetypes.StringType{}},
            + 				state:          2,
            + 			},
            + 		},
            + 		elementType: basetypes.ObjectType{AttrTypes: map[string]attr.Type{"nested_computed": basetypes.StringType{}}},
            + 		state:       2,
            + 	},
              	Diagnostics:     nil,
              	RequiresReplace: s"[]",
              	Private:         nil,
              }

--- FAIL: TestBlockModifyPlan (0.00s)
    --- FAIL: TestBlockModifyPlan/block-list-usestateforunknown-custom-type (0.00s)
        /Users/bflad/src/github.com/hashicorp/terraform-plugin-framework/internal/fwserver/block_plan_modification_test.go:3099: Unexpected response (+wanted, -got):   fwserver.ModifyAttributePlanResponse{
            - 	AttributePlan: types.ListValueWithSemanticEquals{
            - 		ListValue: basetypes.ListValue{
            - 			elements: []attr.Value{
            - 				basetypes.ObjectValue{
            - 					attributes:     map[string]attr.Value{...},
            - 					attributeTypes: map[string]attr.Type{...},
            - 					state:          2,
            - 				},
            - 			},
            - 			elementType: basetypes.ObjectType{AttrTypes: map[string]attr.Type{"nested_computed": basetypes.StringType{}}},
            - 			state:       2,
            - 		},
            - 	},
            + 	AttributePlan: basetypes.ListValue{
            + 		elements: []attr.Value{
            + 			basetypes.ObjectValue{
            + 				attributes:     map[string]attr.Value{"nested_computed": basetypes.StringValue{...}},
            + 				attributeTypes: map[string]attr.Type{"nested_computed": basetypes.StringType{}},
            + 				state:          2,
            + 			},
            + 		},
            + 		elementType: basetypes.ObjectType{AttrTypes: map[string]attr.Type{"nested_computed": basetypes.StringType{}}},
            + 		state:       2,
            + 	},
              	Diagnostics:     nil,
              	RequiresReplace: s"[]",
              	Private:         nil,
              }

--- FAIL: TestBlockPlanModifyList (0.00s)
    --- FAIL: TestBlockPlanModifyList/response-planvalue-custom-type (0.00s)
        /Users/bflad/src/github.com/hashicorp/terraform-plugin-framework/internal/fwserver/block_plan_modification_test.go:3528: unexpected difference:   &fwserver.ModifyAttributePlanResponse{
            - 	AttributePlan: basetypes.ListValue{
            - 		elements:    []attr.Value{basetypes.StringValue{state: 2, value: "testvalue"}},
            - 		elementType: basetypes.StringType{},
            - 		state:       2,
            - 	},
            + 	AttributePlan: types.ListValueWithSemanticEquals{
            + 		ListValue: basetypes.ListValue{
            + 			elements:    []attr.Value{basetypes.StringValue{state: 2, value: "testvalue"}},
            + 			elementType: basetypes.StringType{},
            + 			state:       2,
            + 		},
            + 	},
              	Diagnostics:     nil,
              	RequiresReplace: s"[]",
              	Private:         nil,
              }

[austinvalle]

Thank you for breaking up the changeset 😆 - Looks good to me 👍🏻

[github-actions]

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