Split the mods, layout, leds parts of xkb_state_components

Split the mods, layout, leds parts of xkb_state_components

Note first:
This commits breaks the ABI somewhat. If an application is run against
this commit without recompiling against the updated header, these break:
    - xkb_state_layout_*_is_active always retuns false.
    - xkb_state_serialize_mods always returns 0.
So it might break layout switching in some applications. However,
xkbcommon-compat.h provides the necessary fixes, so recompiling should
work (though updating the application is even better).

Split the enum to its individual components, which enables us to refer
to them individually. We will use that later for reporting which
components of the state have changed after update.

Signed-off-by: Ran Benita <ran234@gmail.com>