Prepare for complete localization

[defagos]

Description

This PR prepares the PillarboxPlayer and PillarboxCoreBusiness libraries for localization. Remaining translations still must be requested and integrated in a future PR.

Changes made

• Fix playback errors not being correctly detected anymore after Support standard actions at item playback end #780.
• Revisit error management to ensure that all error messages are properly localized. The debug description is checked before having a look at an item error log, since errors associated with items are often better localized (errors in the errro log are still useful and localized, though, especially custom errors thrown by resource loaders).
• Remove several keys for which translation is not needed.
• Prepare files, translations and screenshots on Crowdin.

Only a single key is set to manual mode in the string catalog (string which belongs to the iOS code only and which would otherwise be removed when compiling for tvOS).

Note that the code has been tested on iOS 17 and 16 (simulator only). The new error management works fine.

Checklist

• APIs have been properly documented (if relevant).
• The documentation has been updated (if relevant).
• New unit tests have been written (if relevant).
• The demo has been updated (if relevant).