Add Alias to Mask announcement strings

[codemist]

[Vinnl]

I added 9860974 to this so we can fix this: mozilla/fx-private-relay#1738 (comment), hope you don't mind. It's an alt text for the "This link opens in a new tab" icon:

Other strings look good to me.

[Vinnl]

(Small heads-up that I shortened the alt text I added as per an a11y recommendation, to make screen readers less verbose: b2f1f9f.)

Edit: and also a3bd0cc to add parentheses, as OK'd by a11y. (Note that I'm only adding these because it wasn't merged yet, otherwise it'd have been fine as-is.)

[peiying2]

Looks good. I will let you merge whenever you are ready or wait for more strings to consolidate on the PRs.

[flodolo]

What about locales who didn't change the translation from alias to mask? There's no way to work around this…