[Dropped FF92] [Media] AVIF support

[Rumyra]

Enable AVIF support by default Looks like AVIF support is finally here

Acceptance Criteria

• The listed features are documented sufficiently on MDN
• BCD is updated
• Interactive example and data repos are updated if appropriate
• The content has been reviewed as needed

For folks helping with Firefox related documentation

• Set bugs to dev-doc-complete
• Add entry to Firefox release notes if feature is enabled in release
  or
• Add entry to Firefox experimental features page if feature is not yet enabled in release

Features to document

• AVIF support is enabled by default

Related Gecko bugs

• Enable AVIF support by default

Other

Fixes #1726

[hamishwillee]

Status

• Remove from Experimental Features page - FF92 AVIF: Remove experimental feature and update accept headers. #7873
• Docs - Release notes - FF92: AVIF - relnote and image updates #8005
• Docs: List of default accept values - FF92 AVIF: Remove experimental feature and update accept headers. #7873
• Docs: Tidy up pagemacro inclusion of image guide before doing other work: Remove pagemacro inclusion of image guide in HTML>Element>img #7996
• Docs: Image guide - version info
• New pref: FF92: AVIF - relnote and image updates #8005
• BCD - Not doing as no docs on media formats in BCD. This is done in the media format docs itself.
• dev-docs-complete - https://bugzilla.mozilla.org/show_bug.cgi?id=1682995#a21027849_506079

[hamishwillee]

I think this is all good/ready to review

[Rumyra]

Brill - thanks so much @hamishwillee 👍