Add runtime async tests for catching non-Exception throws

[Copilot]

Runtime async (async2) is meant to match compiler state-machine async (async1). No coverage existed for catching objects that don't derive from System.Exception (only throwable via IL), where RuntimeCompatibilityAttribute(WrapNonExceptionThrows) governs whether the object surfaces as a RuntimeWrappedException. These tests close that hole and pin down where the two forms agree and diverge.

Description

New tests under src/tests/async/runtime-wrapped-exception/:

• NonExceptionThrower.il — IL helper that throws a non-Exception object (a string), since C# can't express this.
• NoWrapThrowers.cs — helper assembly marked [assembly: RuntimeCompatibility(WrapNonExceptionThrows = false)] with async1/async2 throwers. The attribute is assembly-scoped, so an opt-out variant requires its own assembly.
• runtime-wrapped-exception.cs — awaits each thrower (async1 via [RuntimeAsyncMethodGeneration(false)], async2 by default) and asserts the caller observes a RuntimeWrappedException wrapping the thrown object, for throws both before and after a suspension point, under both WrapNonExceptionThrows settings.

Observed behavior:

• WrapNonExceptionThrows = true (C#/CoreLib default): async1 and async2 match — caller sees RuntimeWrappedException in all cases.
• WrapNonExceptionThrows = false: they match for a synchronous (pre-yield) throw and for async2 after a yield. They diverge for a non-Exception thrown after a suspension point — async2 faults the Task with a RuntimeWrappedException, while async1 lets the raw object escape onto the thread pool and crash the process.

The divergent (crashing) case, CatchAfterYield_NoWrap_Async1, is disabled with [ActiveIssue("https://github.com/dotnet/runtime/issues/123194")], which unconditionally skips it and keeps it out of the merged runner so it can't abort the process. The remaining 7 tests run.

// async1 (state machine) vs async2 (runtime async) — same body, different generation
public static async Task ThrowAfterYieldAsync2()
{
    await Task.Yield();
    NonExceptionThrower.ThrowNonException(); // throws a string (IL)
}

[RuntimeAsyncMethodGeneration(false)]
public static async Task ThrowAfterYieldAsync1()
{
    await Task.Yield();
    NonExceptionThrower.ThrowNonException();
}

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Pull request overview

Copilot reviewed 6 out of 7 changed files in this pull request and generated 1 comment.

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[VSadov]

@copilot per suggestion from @MichalStrehovsky, please use #69919 for blocking the test on NativeAOT. (the issue already covers general scenarios with non-Exception throws on NativeAOT)

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[Copilot]

@copilot per suggestion from @MichalStrehovsky, please use #69919 for blocking the test on NativeAOT. (the issue already covers general scenarios with non-Exce...

Updated in the latest commit — the NativeAOT blocking comment now references #69919.

[VSadov]

@copilot there is ‎reflect_ai.csx in the changes with only whitespace changes. I think that should be reverted.

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[Copilot]

@copilot there is ‎reflect_ai.csx in the changes with only whitespace changes. I think that should be reverted.

Removed in the latest commit.

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