Bug 1728472 - Part 2: Restrict advertised languages in MSIX to allow-list from...

Bug 1728472 - Part 2: Restrict advertised languages in MSIX to allow-list from Windows. r=bhearsum,flod

Windows MSIX packages support a finite set of locales: see
https://docs.microsoft.com/en-us/windows/uwp/publish/supported-languages.
This patch encodes that list in
browser/installer/windows/msix/msix-all-locales.  Two ad-hoc
modifications were necessary: removing 'sr*' (Serbian) and 'uz*'
(Uzbek) in order for the resulting MSIX packages to install.

We distribute all of the langpacks supported by the release channel in
our MSIX, which is encoded in browser/locales/all-locales.  But we
only advertise support in the App manifest for the intersection of
that set and the set of locales supported by Windows.

We do so to avoid the following issue.  Suppose a user manually
installs a langpack that is not supported by Windows, and then updates
the installed MSIX package.  MSIX package upgrades are essentially
paveover installs, so there is no opportunity for Firefox to update
the langpack before the update.  But, since all langpacks are bundled
with the MSIX, that langpack will be up-to-date, preventing one class
of YSOD.

Differential Revision: https://phabricator.services.mozilla.com/D126175