Add more *Text functions from xkbfile

Add more *Text functions from xkbfile

This should cover all the usage in xkbcomp. The format arguments were
dropped except for the special case of XkbModMaskText, which needs to
write in XkbCFile format in HandleVModDef. This was just changed to a
Bool to avoid the need for the macros in XKBfile.h.

The function prefixes have been renamed to be unique from xkbfile.