* Honor author-specified [Overload] names in the WinMD generator

Port custom overload name support from PR #2275 (CsWinRT 2.x) to the
CsWinRT 3.0 WinMD generator (cswinrtwinmdgen). When an authored method
carries [Windows.Foundation.Metadata.Overload("Name")], emit that name in
the generated .winmd instead of an auto-generated sequential one. windows-rs
consumers require explicit overload names because Rust has no method overloading.

- Record author-specified overload names while emitting interface methods and
  honor them in AddOverloadAttributesForType; stop copying the [Overload]
  attribute verbatim so it is never duplicated.
- Select the default overload (which keeps the original name) from the
  [DefaultOverload] attribute rather than metadata order, so an author-specified
  name is not dropped when the default is not declared first.
- Auto-generated names skip any name already used by another method or an
  author-specified overload, avoiding collisions.
- Emit [Overload] only on interfaces (authored and synthesized), matching the
  Windows Runtime metadata convention; runtime classes expose their ABI through
  interfaces (consistent with CsWinRT 2.x).

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Port custom overload name tests from PR #2275

Add the ICustomOverloadNames interface and CustomOverloadNamesClass authoring
types, and the CustomOverloadNames consumption test. The test validates that
author-specified [Overload] names (LookupByIndex, LookupByFlag, TransformNumber)
appear in the generated projection's ABI vtables, on both an authored interface
and a class's synthesized interface.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

* Add overload-name coverage for auto-generation, collisions, and default selection

Extend the overload-name tests to cover behaviors beyond the original PR:

- Verify the auto-generated ABI name (Transform2) coexists with an author-
  specified one (TransformNumber) in the same overload group.
- OverloadCollisionClass: an author-specified overload name matching the auto
  pattern ("M2") forces the auto-generated name of the remaining overload to
  skip it ("M3").
- DefaultOverloadNotFirstClass / IDefaultOverloadNotFirst: [DefaultOverload] on
  a non-first overload keeps the original ABI name, while the author-specified
  name ("GetByIndex") on the first overload is still honored.

Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

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Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>