fix: Add ability to switch to expression when editing an "OpenObjectField" (object with additionalProperties) & only show OpenObjectField when additionalProperties is an object

[LouisEugeneMSFT]

Description

• Adding ability to switch to an expression from an OpenObjectField when the schema permits it.
• Showing OpenObjectField when additionalProperties is an object, not any truthy value.

Task Item

closes #4599

Screenshots

[cwhitten]

@LouisEugeneMSFT please fix the unit tests:

FAIL packages/adaptive-form/src/utils/tests/resolveFieldWidget.test.ts (6.783 s)
● resolveFieldWidget › type: object › returns OpenObjectField when additional properties are allowed

expect(received).toEqual(expected) // deep equality

Expected: [Function OpenObjectField]
Received: [Function anonymous]

  220 | 
  221 |       const { field: ReturnedField } = resolveFieldWidget({ schema });
> 222 |       expect(ReturnedField).toEqual(DefaultFields.OpenObjectField);
      |                             ^
  223 |     });
  224 |   });
  225 | 

  at Object.toEqual (src/utils/__tests__/resolveFieldWidget.test.ts:222:29)

[coveralls]

Coverage increased (+0.006%) to 55.14% when pulling c0bceb3 on leugene/issue4599 into 8589c32 on main.