Add MethodDesc comments

[noahfalk]

Added clarifying comments on some MethodDesc APIs related to TransientIL and diagnostics.

Fyi @rcj1 @davidwrighton @hoyosjs @jkotas
This is a follow up to #120982

[Copilot]

Pull Request Overview

This PR adds clarifying documentation comments to MethodDesc APIs in the CoreCLR VM to explain their behavior with respect to TransientIL and diagnostics. The changes help distinguish between different categories of runtime-generated methods (DynamicMethodDesc, TransientIL, ILStubs) and clarify when methods should be hidden from diagnostic tools.

Key Changes

• Added reminder comment in TryGenerateTransientILImplementation to keep diagnostics filtering in sync when adding new transient IL methods
• Documented that IsDynamicMethod() only returns true for DynamicMethodDesc, not all runtime-generated IL
• Clarified that IsILStub() only detects a subset of IL stubs (those using DynamicMethodDesc)

Reviewed Changes

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

File	Description
src/coreclr/vm/prestub.cpp	Adds comment reminding developers to update IsDiagnosticsHidden() when adding new transient IL methods
src/coreclr/vm/method.inl	Documents the scope and limitations of IsDynamicMethod(), IsILStub(), and IsDiagnosticsHidden() methods

[noahfalk]

/ba-g this was already good prior to rebasing and its not worthwhile to re-run all the CI again.