Prepare switch to mozilla84 for mobile

This is the parent ticket for all the work to switch to mozilla84/fenix84

• application-services#3
• tor-browser-bundle-testsuite#40011 (closed)
• android-components#40027 (closed)
• android-components#40029 (closed)
• fenix#40119 (closed)
• fenix#40120 (closed)
• fenix#40124 (closed)
• tor-browser-build#40155 (closed)
• tor-browser-build#40156 (closed)
• #40236 (closed)
• #40237 (closed)
• #40238 (closed)
• #40239 (closed)
• #40240 (closed)
• #40258 (closed)
• tor-browser-spec#40008 (closed)

Upstream Android rollout: https://bugzilla.mozilla.org/show_bug.cgi?id=1678401