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/unit_test.c

@@ -145,6 +145,8 @@ static const struct ct_test tests[] = {
 	{ "xim/callback-transfer", xim_adapter_callback_transfer },
 	{ "xim/callback-owner-loss", xim_adapter_callback_owner_loss },
 	{ "xim/commit-encoding", xim_adapter_commit_encoding },
+	{ "wl/modifier-mask", wl_modifier_mask },
+	{ "wl/forwarded-keys", wl_forwarded_keys },
 };
 #else
 static const struct ct_test tests[] = {