fix[devtools/extension]: added a workaround for proxy content script injection in firefox (#27375)

Changes:
1. [Firefox-only] For some reason, Firefox might try to inject
dynamically registered content script in pages like `about:blank`. I
couldn't find a way to change this behaviour, `about:` is not a valid
scheme, so we can't exclude it and `match_about_blank` flag is not
supported in `chrome.scripting.registerContentScripts`.
2. While navigating the history in Firefox, some content scripts might
not be re-injected and still be alive. To handle this, we are now
patching `window` with `__REACT_DEVTOOLS_PROXY_INJECTED__` flag, to make
sure that proxy is injected and only once. This flag is cleared on
`pagehide` event.