[LangRef] Fix the documentation of wchar_size/min_enum_size metadata (#241540)
5dc2934b introduced these metadata module flags, but documented
something else -- `short_wchar` and `short_enum`, which not only differ
in names, but also in the meaning of their values.
The text also presented the flags as ARM-specific. This has changed for
`wchar_size` long ago (it has been used by TLI for quite a while).
Still true for `min_enum_size`.
Assisted-by: Claude