Resolve keysyms early in parser

Resolve keysyms early in parser

Instead of having the parser passing strings to the AST, and
symbols/compat etc. resolving them themselves. This simplifies the code
a bit, and makes it possible to print where exactly in the file the bad
keysym originates from.

The previous lazy approach had an advantage of not needlessly resolving
keysyms from unrelated maps. However, I think reporting these errors in
*any* map is better, and the parser is also a bit smarter then old
xkbcomp and doesn't parse many useless maps. So there's no discernible
speed/memory difference with this change.

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