Internally "key repeat" is reword into "long press" when the same
mechanism was used for both features.
The constraint that 'timeoutWhat' must be set to '-1' when no message is
expected has been lifted to simplify the code.
The long press timeout is used for long press on keys that do not
repeat, for example the keyboard switching key.
This must be detached from the key repeat as it might be disableable in
the future and more keys might be longpressable.
This makes translation easier as there's a single file to edit at.
Existing short and full descriptions are conserved.
sync_translations.py takes care of updating the metadata files.
The metadata directories are renamed to match the language codes used in `res/`.
Contributing guidelines are updated accordingly.
