Prepare switch to mozilla91

• # (Rebase tor-browser patches to 91.0bX)
• tor-browser-build# (Make the list of components updates for switch to mozilla91-based Fenix)
• tor-browser-build# (Update components for switch to mozilla91-based Fenix)
• # (Review developer notes for Firefox 91)
• # (Review GeckoView Changelog for gv91)
• # (Review closed mozilla91 bug)
• android-components# (Rebase android-components patches for Fenix 91 beta X builds)
• android-components# (Review MozAC Changelog for Fenix91)
• fenix# (Rebase Fenix patches to Fenix 91 beta X)
• tor-browser-spec# (FF91 network audit)
• tor-browser-bundle-testsuite# (Update tests when switching to Fenix 91)
• fenix# (Review changes for Fenix91)
• #40522 (closed) (Revert (part of) 1661517)