Split React DevTools into individual panels

[huntie]

Summary

Split the previous React DevTools panel into two individual panels, matching the current Chrome extension on web.

  front_end/panels/react_devtools/
  ├── BUILD.gn
+ ├── ReactDevToolsComponentsView.ts
  ├── ReactDevToolsModel.ts
+ ├── ReactDevToolsProfilerView.ts
+ ├── ReactDevToolsViewBase.ts
  ├── react_devtools.ts
+ ├── react_devtools_components-meta.ts
+ └── react_devtools_profiler-meta.ts

Key changes:

• Updates React DevTools artifacts to be based on [DevTools] Separate RDT Fusebox into single-panel entry points facebook/react#30708 (stacked from React DevTools 5.3.0 (facebook/react@1434af3).
• Adds separate entry points extending ReactDevToolsViewBase.
• Moves ownership of wall, bridge, store, listeners into ReactDevToolsModel (to share across each panel).
  • This uses an ensureInitialized/isInitialized pattern to run ReactDevToolsBindingsModel side-effects once.
• Refactors ReactDevToolsViewBase to use the SDKModelObserver (modelAdded) pattern to reduce boilerplate.

Test plan

🎬 https://pxl.cl/5tXQp

✅ ⚛️ Elements panel: Working Element highlighting and mouse hovering/panel focus changes
✅ Switching to another panel and back preserves highlighted element and scroll position (no re-mounting)
✅ ⚛️ Profiler panel: Switching to panel initialises correctly, profile can be taken
✅ Reload behaviour: Both panels reset and load (in reverse order)

Upstreaming plan

• This commit should be sent as a patch to the upstream devtools-frontend repo. I've reviewed the contribution guide.
• This commit is React Native-specific and cannot be upstreamed.

[hoxyq]

TypeScript supports private keyword, and it is far more popular than # in this codebase. I don't have a strong opinion on this, but would prefer sticking to a single style across the whole codebase.

Is there a specific reason to use # over private?

[huntie]

Yeah, functionally # will act as private members at runtime, added to JS later than TypeScript's private (which will simply do a compile time check). We definitely don't need to replace everywhere, but I'd prefer this convention in RN-unique files.