Bug 40679&40713: Inject torbutton translations in tor-browser-build and always use the most fresh translations for nightly builds

We are finally moving to Weblate!

As a consequence, we group all files in a single branch, and injecting them directly from tor-browser-build becomes possible.

However, I wonder if we could use only a single project for all translations.

Also, since I was at it, I've updated the other translation projects to fetch using the branch name in nightlies, so translators can have a quicker feedback.

Closes #40679 (closed) #40713 (closed).

/cc @boklm