AVIF fallback to integration for transparency

[chcunningham]

Hi!

In #4807 and #5140, the platform AVIF decoder may not support transparency, so use of the integration library is recommended. Is there a smart way for me to setup the integration library as a runtime fallback for AVIF that uses transparency, while continuing to use the platform library for opaque AVIF? The underlying assumption here is that the platform library may perform better when hw acceleration is supported.

Thanks!