feat: add basic vim navigation to urlbar

[adrianord]

Adds the keybinds ctrl+j and ctrl+k to down and up respectively when the urlbar is active for making selections.

This change adds:

• Preference for activating vim navigation for backwards compatibility
• Patch for activating the preference
• IDs in the locales for the preference
  • Localization is all in English, but I am happy to go back and try to translate a few if that helps, just not my strong suit.

Tested on MacOS and Ubuntu (Parallels)

Behavior we see:

• ctrl+j and ctrl+k take precedence when the urlbar is active
• keybinds bound to ctrl+j and ctrl+j still work while the urlbar is not active

zen-urlbar-vim-navigation-1080.mov

[mr-cheffy]

Could there please be some unit tests about this to make sure future firefox versions dont break this functionality?

[adrianord]

@mr-cheffy I've gone ahead and written a unit test for the vim navigation feature.

It's a little crude, so let me know if you have a better way to force multiple possible selections in the URLBar more reliably. What I've done works, but I'm afraid it might be a little brittle, so I'll leave it up to your judgement.

[adrianord]

Rebased to fix conflicts, is there anything else that needs to be done in this PR before it can get reviewed?

[adrianord]

Updated the PR to remove the option from Preferences to keep it just in about:config, removed the localization since that was only used for the Preferences checkbox, and added the test for when the about:config option is turned off.