Remove reflection from UICultureUtilities

[Copilot]

UICultureUtilities.cs used reflection to discover and invoke the CultureInfo.CurrentUICulture setter (falling back to Thread.CurrentThread.CurrentUICulture) because the setter wasn't universally available when the code was written. The API is now directly accessible in .NET Standard 2.0+.

Changes

• Deleted TryGetCurrentUICultureSetter and TryGetCurrentThreadUICultureSetter reflection helpers, the static constructor, s_setCurrentUICulture field, and currentUICultureName constant
• Replaced indirect s_setCurrentUICulture(value) calls with CultureInfo.CurrentUICulture = value
• Removed the null-setter early-return guard from all three WithCurrentUICulture overloads (no longer needed since the setter is always available)
• Dropped using System.Diagnostics.CodeAnalysis and using System.Reflection

Before:

// ~100 lines of reflection scaffolding to conditionally find and invoke the setter
private static readonly Action<CultureInfo>? s_setCurrentUICulture;
// ...
s_setCurrentUICulture(savedCulture);

After:

CultureInfo.CurrentUICulture = savedCulture;

Microsoft Reviewers: Open in CodeFlow

[jasonmalinowski]

Hah nice!