Mark custom continuation resumptions as StackTraceHidden

[jakobbotsch]

E.g.

public static async Task Main()
{
    Task t = ThrowsSoon();
    try
    {
        await t;
    }
    catch (Exception ex)
    {
        Console.WriteLine(ex);
    }
}

private static async Task ThrowsSoon()
{
    await Task.Delay(50);
    throw new Exception("Exception thrown");
}

 System.Exception: Exception thrown
    at Program.ThrowsSoon() in C:\dev\dotnet\playground\Program.cs:line 24
-   at System.Runtime.CompilerServices.RuntimeAsyncTaskContinuation.TaskContinuationResume.ResumeTaskContinuation(Continuation cont, Byte& result)
    at Program.Main() in C:\dev\dotnet\playground\Program.cs:line 13

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[Copilot]

Pull request overview

This PR hides internal async continuation resumption frames from user-visible exception stack traces by marking the relevant resumption helpers as [StackTraceHidden], and adds tests to ensure those frames no longer appear for both Task and ValueTask/IValueTaskSource continuation paths.

Changes:

• Mark RuntimeAsyncTaskContinuation.TaskContinuationResume.ResumeTaskContinuation as [StackTraceHidden].
• Mark AsyncHelpers.ValueTaskSourceContinuation.ValueTaskSourceContinuationResume.ResumeValueTaskSourceContinuation as [StackTraceHidden].
• Extend StackTraceTests with new async scenarios and assertions that "ResumeTaskContinuation" / "ResumeValueTaskSourceContinuation" are absent from Exception.ToString() output.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/libraries/System.Diagnostics.StackTrace/tests/StackTraceTests.cs	Adds new async test cases (Task + custom IValueTaskSource) and asserts resumption helpers don’t appear in exception text.
src/coreclr/System.Private.CoreLib/src/System/Runtime/CompilerServices/RuntimeAsyncTaskContinuation.cs	Adds [StackTraceHidden] to the Task continuation resume helper to suppress it from stack traces.
src/coreclr/System.Private.CoreLib/src/System/Runtime/CompilerServices/AsyncHelpers.ValueTaskSourceContinuation.cs	Adds [StackTraceHidden] to the ValueTaskSource continuation resume helper to suppress it from stack traces.

[Copilot]

Pull request overview

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

[jakobbotsch]

PTAL @rcj1

[jakobbotsch]

/azp run runtime-nativeaot-outerloop

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