wayland: Disable text-input-v3 when it's destroyed

Destroying a zwp_text_input_v3 object should be viewed as disabling it.

isEnabled property is cached because it cannot be computed in
_destroy_resource() handler. By that time, the resource no longer will
be in resourceMap(), so TextInputV3InterfacePrivate::isEnabled() will
erroneously return false even though we expect true.