Key fixes:
- Replace `base::WeakPtrFactory` with `gin::WeakCellFactory` in
MenuMac, MenuViews, and NetLog, since weak pointers to cppgc-managed
objects must go through weak cells
- Replace `v8::Global<v8::Value>` with `cppgc::Persistent<Menu>` for
the menu reference in BaseWindow
- Stop using `gin_helper::Handle<T>` with cppgc types; use raw `T*`
and add a `static_assert` to prevent future misuse
- Add proper `Trace()` overrides for Menu, MenuMac, MenuViews, and
NetLog to ensure cppgc members are visited during garbage collection
- Replace `SelfKeepAlive` prevent-GC mechanism in Menu with a
`cppgc::Persistent` prevent-GC captured in `BindSelfToClosure`
- Introduce `GC_PLUGIN_IGNORE` macro to suppress
known-safe violations: mojo::Remote fields, ObjC bridging pointers,
and intentional persistent self-references
- Mark `ArgumentHolder` as `CPPGC_STACK_ALLOCATED()` in both Electron's
and gin's function_template.h to silence raw-pointer-to-GC-type
warnings
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