Fix MethodBase.GetCurrentMethod with runtime async

[eduardo-vp]

Fixes #122546.

The following code can now be Native AOT compiled and run with runtime-async enabled.

class Program
{
    static async Task Main()
    {
        Console.WriteLine("Hello world");
        await MyAsyncMethod();
    }

    static async Task MyAsyncMethod()
    {
        MethodBase currentMethod = MethodBase.GetCurrentMethod();
        Console.WriteLine($"Current method: {currentMethod?.Name}");
        await Task.Delay(100);
    }
}

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[Copilot]

Pull request overview

This PR attempts to fix an issue where MethodBase.GetCurrentMethod() fails when called from within an async method in Native AOT compilation. The fix adds logic to handle async methods by unwrapping async method variants to get the original method definition before creating the reflection thunk.

Key Changes

• Adds async method handling in the ExpandIntrinsicForCallsite method for MethodBase.GetCurrentMethod() intrinsic expansion
• When the callsite is an async method, the code attempts to get the target of the async variant method before generating the thunk

[MichalStrehovsky]

We also need a test. Conveniently, a test already exists, we just need to remove ActiveIssue (the issue number is wrong):

runtime/src/tests/async/reflection/reflection.cs

Line 250 in c591f97

[ActiveIssue("https://github.com/dotnet/runtime/issues/122517", typeof(TestLibrary.Utilities), nameof(TestLibrary.Utilities.IsNativeAot))]