Symlinks and paths ending with /locale not supported by TextDomain

[sophie-h]

I tried to use TextDomain with flatpak and two issues prevent me from using it:

1. The locale dir passed to the buildsystem ends with /locale. Would be nice if this is supported by TextDomain::prepend as well. (Easy to work around.)
2. Flatpak or Flathub uses symlinks of the form /app/share/locale/es -> ... But TextDomain::init() does not follow symlinks inside locale for the checks. This makes it basically unusable for this case.