Make xkb_map_get_as_string test more comprehensive

Make xkb_map_get_as_string test more comprehensive

Add a test/dump.data file which contains the result we're expecting from
xkb_map_get_as_string run on a particularly complex set of keymaps, and
assert that the string representations are the same.  This means that
any updates to xkb_map_get_as_string will also need to update the test
data, but should also ensure that we don't have any more parser
regressions.

Compared with diff to the output of setxkbmap + xkbcomp for the same
keymap; seems completely solid.

Signed-off-by: Daniel Stone <daniel@fooishbar.org>