compositor: Move repaint debug binding to mod-shift-space

Alt-space or Super-space are too likely to conflict with application
bindings.

src/compositor.c

@@ -1798,6 +1798,8 @@ notify_modifiers(struct wl_seat *wl_seat, uint32_t serial)
 		seat->modifier_state |= MODIFIER_ALT;
 	if (mods_lookup & (1 << seat->xkb_info.super_mod))
 		seat->modifier_state |= MODIFIER_SUPER;
+	if (mods_lookup & (1 << seat->xkb_info.shift_mod))
+		seat->modifier_state |= MODIFIER_SHIFT;
 
 	/* Finally, notify the compositor that LEDs have changed. */
 	if (xkb_state_led_index_is_active(seat->xkb_state.state,

src/compositor.h

@@ -52,6 +52,7 @@ enum weston_keyboard_modifier {
 	MODIFIER_CTRL = (1 << 0),
 	MODIFIER_ALT = (1 << 1),
 	MODIFIER_SUPER = (1 << 2),
+	MODIFIER_SHIFT = (1 << 3),
 };
 
 enum weston_led {

src/shell.c

@@ -3248,7 +3248,7 @@ shell_add_bindings(struct weston_compositor *ec, struct desktop_shell *shell)
 					  ec);
 	weston_compositor_add_key_binding(ec, KEY_BRIGHTNESSUP, 0,
 				          backlight_binding, ec);
-	weston_compositor_add_key_binding(ec, KEY_SPACE, mod,
+	weston_compositor_add_key_binding(ec, KEY_SPACE, mod | MODIFIER_SHIFT,
 				          debug_repaint_binding, shell);
 	weston_compositor_add_key_binding(ec, KEY_K, mod,
 				          force_kill_binding, shell);