Draft: wlr_output: Introduce wlr_output_test_capabilities

wlr_output_test_capabilities makes it possible to check if an output provides the features used by a particular wlr_output_state. This is useful for checking if e.g. adaptive sync, gamma or a particular render format is supported.

This differs from wlr_output_test_state(), which tests if a configuration will apply successfully given the current system state, rather than whether the capability is generally supported.

This was the first thing that came to mind to let compositors probe various output capabilities such as adaptive sync, which is useful both to advertise capabilities to the user and to avoid wasting time probing nonsensical configurations.