See #80828 and the internals@ mailing list discussion at
https://externals.io/message/116543
Use libavifinfo's AvifInfoGetFeaturesStream() in php_handle_avif() to
get the width, height, bit depth and channel count from an AVIF
payload. Implement stream reading/skipping functions and data struct.
Use libavifinfo's AvifInfoIdentifyStream() in php_is_image_avif().
Update the expected features read from "test1pix.avif" in
getimagesize.phpt.
Closes GH-7711.
