weston_xkb_info: Cache all modifier indices for X11

X11 has a set of eight modifiers which we want to represent.  Cache
their indices when we create a weston_xkb_info, so we can use this from
compositor-x11 to keep the state synchronised exactly between the host X
server and a nested Weston instance.

Signed-off-by: Daniel Stone <daniel@fooishbar.org>
diff --git a/src/compositor.h b/src/compositor.h
index 3bf68dc..f87843a 100644
--- a/src/compositor.h
+++ b/src/compositor.h
@@ -189,9 +189,14 @@
 	int keymap_fd;
 	size_t keymap_size;
 	char *keymap_area;
+	xkb_mod_index_t shift_mod;
+	xkb_mod_index_t caps_mod;
 	xkb_mod_index_t ctrl_mod;
 	xkb_mod_index_t alt_mod;
+	xkb_mod_index_t mod2_mod;
+	xkb_mod_index_t mod3_mod;
 	xkb_mod_index_t super_mod;
+	xkb_mod_index_t mod5_mod;
 	xkb_led_index_t num_led;
 	xkb_led_index_t caps_led;
 	xkb_led_index_t scroll_led;