Drop size of hello world to 745 kB

[MichalStrehovsky]

(With StackTraceSupport=false, OptimizationPreference=Size, UseSystemResourceKeys=true)

I don't know if we want it in this form, but it is tempting. The thing that makes the difference is that we are no longer boxing enums and we can get rid of the super expensive enum stringification logic.

Not boxing enums also means that #118640 can fully kick in because enums are the last remaining place that looks at custom attributes (looking for FlagsAttribute).

Cc @dotnet/ilc-contrib

[Copilot]

Pull Request Overview

This PR aims to reduce the size of hello world applications to 745 kB by eliminating enum boxing and expensive enum stringification logic. The changes focus on optimizing enum handling in the NativeAOT runtime to enable better size optimizations.

Key changes:

• Avoids enum boxing by using direct value comparisons and explicit casts
• Replaces enum ToString() calls with hardcoded string switch expressions
• Refactors methods to bypass enum validation when internal consistency is guaranteed

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
CultureData.cs	Replaces enum array initialization with cast from ushort array to avoid boxing
Thread.NativeAot.Windows.cs	Changes method visibility and replaces enum ToString() with switch expression
GC.NativeAot.cs	Refactors to bypass enum validation in internal calls
MethodTable.Runtime.cs	Optimizes enum detection logic using direct type comparison
StartupCodeHelpers.Extensions.cs	Uses internal unchecked method to avoid enum validation overhead

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[jkotas]

This looks reasonable to me. The unnatural patterns need comments to make it clear why they are needed.