test/libmpv: use common wrappers for properties and commands

This is mainly for better, more descriptive logging when something goes
wrong and fails. Common operations that manipulate properties and
commands go through shared functions that do better detailed logging.
Also it means we don't need check_api_error around anymore so get rid of
that. libmpv_lifetime is left untouched since that one is a bit special
and works a little differently.