Don't limit key names to 4 characters

Don't limit key names to 4 characters

Currently you can't give a key in xkb_keycodes a name of more than
XKB_KEY_NAME_LENGTH (= 4) chars. This is a pretty annoying and arbitrary
limitation; it leads to names such as <RTSH>, <COMP>, <PRSC>, <KPAD>
etc. which may be hard to decipher, and makes it impossible to give
more standard names (e.g. from linux/input.h) to keycodes.

The purpose of this, as far as I can tell, was to save memory and to
allow encoding a key name directly to a 32 bit value (unsigned long it
was).

We remove this limitation by just storing the names as atoms; this lifts
the limit, allows for easy comparison like the unsigned long thing, and
doesn't use more memory than previous solution. It also relieves us from
doing all of the annoying conversions to/from long.

This has a large diffstat only because KeyNameText, which is used a lot,
now needs to take the context in order to resolve the atom.

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