Add new internal API: enableOptionalCodecs()/disableOptionalCodecs()

This API can be used to enable the optional codecs, or disable them
and use only the mandatory SBC.
Internally, it is implemented by raising the SBC priority to
highest (so SBC will be used/selected), or reducing the SBC priority
to its default value (lowest).

Test: A2DP streaming and enabling/disabling/selecting optional codecs
Bug: 35873828
Change-Id: Ia82036ac33590a3a402b1f5a36102264d47a9029