Simplify the `TranslationProvider` localizations locator

[hailstorm75]

Currently, the TranslationProvider requires a string parameter with the name of the XML file containing the localizations.

The goal is to remove that and let the source generator handle that automatically.
This, however, introduces a potential issue where a single project can have multiple XML files.
This means that the generators must separate the translations based on their defined namespaces.