[Cherry-Pick] Update Requires-Python: >=3.9 (#8886)

[Cherry-Pick] Update Requires-Python: >=3.9 (#8886)

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

…extra-decoders repo (#8800)

Co-authored-by: atalman <[email protected]>

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

…extra-decoders repo (#8800)

Co-authored-by: atalman <[email protected]>

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

…extra-decoders repo (#8800)

Co-authored-by: atalman <[email protected]>

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

…extra-decoders repo (#8800)

Co-authored-by: atalman <[email protected]>

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

…extra-decoders repo (#8800)

Co-authored-by: atalman <[email protected]>

Update pre_build_script.sh

[Cherry-pick for 0.21] Fix doc of masks_to_boxes (#8798) (#8799)

[Cherry-pick for 0.21] Fix doc of masks_to_boxes (#8798) (#8799)