vd_lavc: try other hwdecs when falling back after an hwdec failure

Today, if hwdec initialisation succeeds, we move on to attempting
decoding, and if decoding fails, we enter a fallback path that will
only do software decoding.

This is suboptimal because some hwdecs and codec combinations can
pass hwdec init, but then fail at hwaccel init, or even frame decoding.
In these situations, we will never attempt other hwdecs in the `auto`
or manually specified lists which might work.

One good example is someone tries to use `vulkan,auto` and tries to
play av1 content. The vulkan decoding will fail at hwaccel init time,
and then fallback to software instead of going through the auto list
which would allow vaapi, nvdec, etc to play the file.

Instead, let's not give up immediately, and try the next hwdec after
a failure, just like we do if hwdec init fails.

The key part of this change is to keep track of the hwdecs we have
tried, so that each time we run through hwdec selection, we don't try
the same one over and over again. If we really get through the whole
list with no success, we will then fall back to software decoding.

Fixes #11865

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