[Cherry-pick for 0.21] Migrate avif and heic decoders to torchvision-extra-decoders repo

[NicolasHug]

CP of #8671

I created the release/0.21 a few minutes before I landed #8671 on main, so this needs to be cherry-picked. This is by design: I need to closely monitor any potential issue with that specific PR, that's why I didn't land it on main before the branch cut. So, this is definitely not a "last minute rushed cherry-pick", it's 100% supposed to be part of this release, and having it as a CP helps debugging any potential problem.

[pytorch-bot]

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🧪 See artifacts and rendered test results at hud.pytorch.org/pr/pytorch/vision/8800

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✅ You can merge normally! (1 Unrelated Failure)

As of commit 422d919 with merge base a9a726a ():

BROKEN TRUNK - The following job failed but were present on the merge base:

👉 Rebase onto the `viable/strict` branch to avoid these failures

• Tests / unittests-windows (3.9, windows.g5.4xlarge.nvidia.gpu, cuda, 11.8) / windows-job (gh) (trunk failure)
  AttributeError: '_OpNamespace' 'image' object has no attribute '_jpeg_version'

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[NicolasHug]

I triggered 422d919 yesterday and everything is green (apart from unrelated windows GPU issue which is long-standing and unrelated).