Add directive-argument opt-in and code-first directive APIs

[glen-84]

Summary

• Directive arguments now participate in opt-in features: @requiresOptIn on a directive argument is validated (rejected on required, non-null arguments without a default), filtered via includeOptIn on __Directive.args, and aggregated into __schema.optInFeatures.
• New code-first directive APIs: apply directives to directive arguments (IDirectiveArgumentDescriptor.Directive<T>()), mark a directive argument opt-in (.RequiresOptIn(feature)), register directive types via a configure delegate (AddDirectiveType(Action<IDirectiveTypeDescriptor>) on both ISchemaBuilder and IRequestExecutorBuilder), and configure directive arguments inline (IDirectiveTypeDescriptor.Argument(name, Action<IDirectiveArgumentDescriptor>)).
• Simplified existing AddDirectiveType(new DirectiveType(d => …)) call sites to the new lambda overload.

Test plan

• Directive-argument opt-in: validation rejects @requiresOptIn on required directive arguments; __Directive.args(includeOptIn:) filtering; optInFeatures aggregation includes directive-argument features.
• Code-first: .Directive() and .RequiresOptIn() on directive arguments; AddDirectiveType(Action<…>) registration with an argument configurator.
• Verified the affected suites on net10.0 (Types.Tests, Execution.Tests, Validation.Tests, Types.Mutations.Tests).

[Copilot]

Pull request overview

This PR expands HotChocolate’s directive model by bringing directive arguments into the existing opt-in feature system (@requiresOptIn) and by adding code-first APIs for defining directive types and configuring directive arguments more fluently.

Changes:

• Extend opt-in feature handling to directive arguments (validation, introspection filtering via __Directive.args(includeOptIn:), and aggregation into __schema.optInFeatures).
• Add code-first directive APIs: directive-argument configuration via IDirectiveTypeDescriptor.Argument(name, Action<...>), directive application on directive arguments, and AddDirectiveType(Action<IDirectiveTypeDescriptor>) overloads on both schema and executor builders.
• Update existing tests/call sites to use the new AddDirectiveType delegate overloads and add coverage for directive-argument opt-in behavior.

Reviewed changes

Copilot reviewed 24 out of 24 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
src/HotChocolate/Core/test/Validation.Tests/ValidationUtils.cs	Updates test helper to use the new AddDirectiveType(Action<...>) overload.
src/HotChocolate/Core/test/Types.Tests/Types/Interceptors/FlagEnumInterceptorTests.cs	Migrates directive type registration to the new lambda-based overload.
src/HotChocolate/Core/test/Types.Tests/Types/EnumTypeTests.cs	Migrates directive type registration to the new lambda-based overload in multiple tests.
src/HotChocolate/Core/test/Types.Tests/Types/DirectiveTypeTests.cs	Migrates directive type registration and adds a test for applying directives to directive arguments.
src/HotChocolate/Core/test/Types.Tests/Types/Directives/RequiresOptInDirectiveTests.cs	Adds code-first opt-in features on directive arguments for snapshot coverage.
src/HotChocolate/Core/test/Types.Tests/Types/Directives/snapshots/RequiresOptInDirectiveTests.BuildSchemaAsync_CodeFirst_MatchesSnapshot.graphql	Updates snapshot to include directive-argument @requiresOptIn.
src/HotChocolate/Core/test/Types.Tests/Extensions/SchemaBuilderExtensions.Types.Tests.cs	Adds test coverage for AddDirectiveType(Action<...>) and adjusts null overload ambiguity.
src/HotChocolate/Core/test/Types.Tests/Configuration/Validation/RequiresOptInValidation.cs	Adds SDL validation tests for @requiresOptIn on directive arguments.
src/HotChocolate/Core/test/Types.Tests/Configuration/Validation/snapshots/RequiresOptInValidation.Must_Not_Appear_On_Required_Directive_Argument.snap	Adds snapshot for the new validation error.
src/HotChocolate/Core/test/Types.Tests/Configuration/TypeTrimmerTests.cs	Migrates directive type registration to the new lambda-based overload.
src/HotChocolate/Core/test/Types.Mutations.Tests/AnnotationBasedMutations.cs	Migrates directive type registration to the new lambda-based overload.
src/HotChocolate/Core/test/Execution.Tests/OptInFeaturesIntrospectionTests.cs	Adds directive-argument opt-in introspection tests and ensures schema opt-in aggregation includes directive-arg features.
src/HotChocolate/Core/test/Execution.Tests/IntrospectionTests.cs	Migrates directive type registration to the new lambda-based overload.
src/HotChocolate/Core/src/Types/Utilities/ErrorHelper.cs	Adds a schema error factory for invalid opt-in usage on required directive arguments.
src/HotChocolate/Core/src/Types/Types/Introspection/__Directive.cs	Adds includeOptIn filtering to __Directive.args when opt-in features are enabled.
src/HotChocolate/Core/src/Types/Types/Interceptors/OptInFeaturesTypeInterceptor.cs	Aggregates opt-in features from directive arguments and supports SDL @requiresOptIn parsing.
src/HotChocolate/Core/src/Types/Types/Directives/RequiresOptInDirectiveExtensions.cs	Adds .RequiresOptIn() support for IDirectiveArgumentDescriptor.
src/HotChocolate/Core/src/Types/Types/Descriptors/DirectiveTypeDescriptor.cs	Adds Argument(name, Action<...>) convenience overload for inline directive-argument configuration.
src/HotChocolate/Core/src/Types/Types/Descriptors/DirectiveArgumentDescriptor.cs	Adds fluent directive-application APIs returning IDirectiveArgumentDescriptor.
src/HotChocolate/Core/src/Types/Types/Descriptors/Contracts/IDirectiveTypeDescriptor.cs	Adds Argument(name, Action<...>) to the public contract.
src/HotChocolate/Core/src/Types/Types/Descriptors/Contracts/IDirectiveArgumentDescriptor.cs	Adds directive-application APIs (Directive(...)) to the public contract.
src/HotChocolate/Core/src/Types/Extensions/SchemaBuilderExtensions.Types.cs	Adds ISchemaBuilder.AddDirectiveType(Action<...>) overload.
src/HotChocolate/Core/src/Types/Execution/DependencyInjection/SchemaRequestExecutorBuilderExtensions.Types.cs	Adds IRequestExecutorBuilder.AddDirectiveType(Action<...>) overload.
src/HotChocolate/Core/src/Types/Configuration/Validation/RequiresOptInValidationRule.cs	Validates @requiresOptIn constraints for directive arguments.

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[github-code-quality]

Code Coverage Overview

Languages: C#

C# / code-coverage/dotnet

The overall coverage in the gai/directive-argume... branch remains at 49%, unchanged from the main branch.

Show a code coverage summary of the most impacted files.

File	main f134fd2	gai/directive-argume... 7f0bf58	+/-
/home/runner/wo...ServerHelper.cs	88%	84%	-4%
/home/runner/wo...geDispatcher.cs	77%	75%	-2%
/home/runner/wo...tocolHandler.cs	84%	83%	-1%
/home/runner/wo...Subscription.cs	90%	92%	+2%
/home/runner/wo...ueryExecutor.cs	65%	67%	+2%
/home/runner/wo...eiveEndpoint.cs	69%	72%	+3%
/home/runner/wo...qlConnection.cs	89%	92%	+3%
/home/runner/wo...erMiddleware.cs	89%	100%	+11%
/home/runner/wo...tionExecutor.cs	56%	70%	+14%
/home/runner/wo...tedDirective.cs	0%	17%	+17%

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