Add AVIF mime type to BitmapFactory

Associate SkEncodedImageFormat::kAVIF to "image/avif" mime type.

Avif mime type can be found in the specification here:
https://aomediacodec.github.io/av1-avif/#mime-registration

Test: Media cts tests still pass.
Test: Invoking ImageDecoder and BitmapFactory with an AVIF image
      returns the correct mime type.
Bug: 141654151
Change-Id: I0b67154a9031e1444912b59757e89cf625ee1280