Add UseSTASynchronizationContext to STATestMethod

[Youssef1313]

Fixes #5729

[Copilot]

Pull request overview

This PR adds a UseSTASynchronizationContext property to STATestMethodAttribute to enable preserving the STA thread context for async continuations. When enabled, the attribute creates a custom SynchronizationContext that ensures async continuations run on the same STA thread, which is useful for testing UI components that require STA threading.

Changes:

• Introduced SingleThreadedSTASynchronizationContext class that manages a dedicated STA thread and routes all operations to it
• Added UseSTASynchronizationContext property to STATestMethodAttribute with default value of false
• Modified STATestMethodAttribute.ExecuteAsync to conditionally use the new synchronization context
• Added tests to verify both default behavior (no sync context) and new behavior (with sync context)

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
src/TestFramework/TestFramework/Attributes/TestMethod/SingleThreadedSTASynchronizationContext.cs	New internal class that implements a custom SynchronizationContext with a dedicated STA thread for routing operations
src/TestFramework/TestFramework/Attributes/TestMethod/STATestMethodAttribute.cs	Added UseSTASynchronizationContext property and modified ExecuteAsync to optionally use the new sync context
src/TestFramework/TestFramework/PublicAPI/PublicAPI.Unshipped.txt	Added public API entries for the new property getter and setter
test/UnitTests/MSTest.SelfRealExamples.UnitTests/STATestMethodSyncContext.cs	Added integration tests verifying both default and new behavior

[Copilot]

Pull request overview

Copilot reviewed 4 out of 4 changed files in this pull request and generated 4 comments.

[Copilot]

Exceptions thrown by the callback in the thread loop are not handled and will terminate the background thread. This could leave queued actions unexecuted and cause hangs in Send calls waiting for done.Set(). Consider wrapping the callback invocation in a try-catch block to handle and potentially log exceptions.

Suggested change

	callback();
	try
	{
	callback();
	}
	catch (Exception ex)
	{
	System.Diagnostics.Debug.WriteLine($"Exception in {nameof(SingleThreadedSTASynchronizationContext)} callback: {ex}");
	}