Add media-type localizations for printer-specific media types (Issue #5168)

Add media-type localizations for printer-specific media types (Issue #5168)

cups/dest-localization.c: Move .strings file loader to language.c.
cups/language-private.h: Add load options for _cupsMessageLoad.
cups/language.c: Move .strings file loader to this file.
cups/ppd-cache.c: Save printer-strings-uri value and load the strings file for m
edia-type
cups/ppd-private.h: Bump cache version and add strings_uri.
locale/checkpo.c: Use _cupsMessageLoad for .strings files.