Add lock key modifier bits input mode

This adds the GLFW_MOD_CAPS_LOCK and GLFW_MOD_NUM_LOCK modifier bits.
Set the GLFW_LOCK_KEY_MODS input mode to enable these for all callbacks
that receive modifier bits.

Fixes #946.

src/mir_window.c

@@ -123,6 +123,10 @@ static int mirModToGLFWMod(uint32_t mods)
         publicMods |= GLFW_MOD_CONTROL;
     if (mods & mir_input_event_modifier_meta)
         publicMods |= GLFW_MOD_SUPER;
+    if (mods & mir_input_event_modifier_caps_lock)
+        publicMods |= GLFW_MOD_CAPS_LOCK;
+    if (mods & mir_input_event_modifier_num_lock)
+        publicMods |= GLFW_MOD_NUM_LOCK;
 
     return publicMods;
 }