Unify some string tables from xkbcomp, text and keymap-dump

Unify some string tables from xkbcomp, text and keymap-dump

We move the LookupEntry struct from expr.h to text.h, along with most of
the lookup tables. This makes them available everywhere.
Looking up a value in the LookupEntry format is slower than direct index
mapping, but it allows multiple names per value (with the canonical one
being first) and "all"- and "none"-type masks. These functions are not
used anywhere efficiency matters.

Signed-off-by: Ran Benita <ran234@gmail.com>