Animate fadeIn of titlebar buttons

[cndouglas]

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Ran git rebase -i to squash commits (if needed).

Test Plan:

1. Make sure "Always show the URL bar" is turned off in preferences.
2. Also make sure "Show Home button on URL bar" is turned on in Preferences.
3. Open a new tab and navigate to any site.
4. Hover over the titlebar.
5. Make sure the reload button and home button fade in with the urlbar.

Fixes #5664

[luixxiul]

Actually I'd prefer this, because there would/could be other buttons added and the buttons name could be changed.

  &:not(.titleMode) {
    .urlbarForm,
    .bookmarkButtonContainer,
    span[class$="Button"] {
      animation: fadeIn .6s;
      opacity: 0;
      animation-fill-mode: forwards;
    }

[cndouglas]

@luixxiul Great! We can close this if you want to submit a PR with that code.

[luixxiul]

You can create another commit, squash two commits, and git push -f to overwrite the commit above.

[cndouglas]

OK, will do.

[cndouglas]

Done. Works fine based on my testing.

[luixxiul]

++

[bsclifton]

Great catch 😄 I tried it out, looks good!

[luixxiul]

This was superseded by #6326