Fix some issues and streamline regeneration process:
- A few glitches (like duplicate language symbols, wrong Windows
language ids etc) were fixed.
- Scripts were added to allow to regenerate the list of supported
locales from the list of known Windows locales.
- Version info when language symbols became available was added to the
documentation of the language symbol enum.
- Synonyms are no longer hard-coded in the script genlang.py.
See #23453.
Closes#23437.
