Bump Electron to 43.0.0

Summary:
Upgrade from Electron 39.0.0 → 43.0.0.

Changelog: [Internal]

**Breaking changes from Electron 39.0.0 → 43.0.0:**

**Electron 40.0.0**
- Deprecated `clipboard` API access from renderer processes (use `contextBridge` from a preload script)
- macOS dSYM debug symbols now compressed with `tar.xz` (`dsym.zip` → `dsym.tar.xz`)

**Electron 41.0.0**
- PDFs no longer create a separate `WebContents` (now render in same WebContents via OOPIFs — use frame tree to detect)
- Cookie `'changed'` event has new causes: `inserted`, `inserted-no-change-overwrite`, `inserted-no-value-change-overwrite`
- Deprecated `showHiddenFiles` in dialogs on Linux (GTK removed the API)

**Electron 42.0.0**
- macOS notifications migrated from `NSUserNotification` to `UNNotification` API (requires code-signed app, else emits `failed` event)
- Offscreen rendering defaults to `1.0` device scale factor (use `webPreferences.offscreen.deviceScaleFactor` to override)
- `electron` npm package no longer downloads via `postinstall` (binary fetched on first `bin` run; `ELECTRON_SKIP_BINARY_DOWNLOAD` removed, use `ELECTRON_INSTALL_PLATFORM` / `ELECTRON_INSTALL_ARCH`)
- Removed `quotas` object from `Session.clearStorageData(options)`

**Electron 43.0.0-alpha.3**
- File downloads will open by default in the user's Downloads folder (or Home directory if Downloads doesn't exist)

Command run:

```
js1 upgrade electron --version 43.0.0-alpha.3
```

Differential Revision: D105587351

Author: huntie

packages/debugger-shell/package.json

@@ -46,7 +46,7 @@
     "fb-dotslash": "0.5.8"
   },
   "devDependencies": {
-    "electron": "39.8.10",
+    "electron": "43.0.0",
     "semver": "^7.1.3"
   },
   "files": [