Add source generator unit tests for invalid JsonExtensionData cases

[layomia]

Some of the serializer tests intentionally define invalid JsonExtensionData properties which would cause InvalidOperationException to be thrown at runtime, e.g.

runtime/src/libraries/System.Text.Json/tests/System.Text.Json.Tests/Serialization/ExtensionDataTests.cs

Lines 300 to 304 in b683032

	private class ClassWithInvalidExtensionProperty
	{
	[JsonExtensionData]
	public Dictionary<string, int> MyOverflow { get; set; }
	}

When source generation is used, compile-time errors are logged rather than deferred to runtime. The PR adding support for JsonExtensionData (#58912) thus disables these tests so that the source generator test project (System.Text.Json.SourceGeneration.Tests) can compile. We should add unit test variants for coverage in System.Text.Json.SourceGeneration.Unit.Tests.

[ghost]

Tagging subscribers to this area: @eiriktsarpalis, @layomia
See info in area-owners.md if you want to be subscribed.

Issue Details

---

Some of the serializer tests intentionally define invalid JsonExtensionData properties which would cause InvalidOperationException to be thrown at runtime, e.g.

runtime/src/libraries/System.Text.Json/tests/System.Text.Json.Tests/Serialization/ExtensionDataTests.cs

Lines 300 to 304 in b683032

	private class ClassWithInvalidExtensionProperty
	{
	[JsonExtensionData]
	public Dictionary<string, int> MyOverflow { get; set; }
	}

When source generation is used, compile-time errors are logged rather than deferred to runtime. The PR adding support for JsonExtensionData (#58912) thus disables these tests so that the source generator test project (System.Text.Json.SourceGeneration.Tests) can compile. We should add unit test variants for coverage in System.Text.Json.SourceGeneration.Unit.Tests.

Author:	layomia
Assignees:	-
Labels:	area-System.Text.Json
Milestone:	7.0.0