test: the xkb modifier mask and the forwarded key bitmap

The two pure things in the Wayland frontend, in the shape the XIM adapter
test already uses: wl.c included behind one define that makes the virtual
keyboard inert, and a keymap built from a string, so no compositor and no
xkb data files are wanted.  The mask test holds Caps Lock apart from
Shift, which is what a Korean key turns on; the bitmap test holds a
release of a key we never passed on, a code the bitmap cannot hold, and
the release of everything still down when the context goes.

wayland-scanner's output is the parent Makefile's to write, as ../strans
already is.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

tests/test.h

@@ -125,3 +125,5 @@ void	xim_adapter_callback_cleanup(struct ct*);
 void	xim_adapter_callback_transfer(struct ct*);
 void	xim_adapter_callback_owner_loss(struct ct*);
 void	xim_adapter_commit_encoding(struct ct*);
+void	wl_modifier_mask(struct ct*);
+void	wl_forwarded_keys(struct ct*);