kimageformats: enable AVIF support

[est31]

Adds the libavif library to build the inputs of kimageformats so that it
can recognize AVIF files.
This enables KDE based apps like gwenview to view avif files.

This patch has been tested as follows: In order for tools like gwenview to even know that it is an avif file, they need to know the mime type. This was done by #126050 which will be pulled into master in #127151. I've rebased this patch onto d90080e and booted a system with that config. I was able to view avif files and thumbnails showed up successfully.

Motivation for this change

closes #125920

Things done

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• 21.11 Release Notes
  • (Package updates) Added a release notes entry if the change is major or breaking
  • (Module updates) Added a release notes entry if the change is significant
  • (Module addition) Added a release notes entry if adding a new NixOS module
• Fits CONTRIBUTING.md.

[r-rmcgibbo]

Result of nixpkgs-review pr 127862 at 69d9445 run on aarch64-linux 1

1 package failed to build:

• libsForQt512.kimageformats

3 packages built successfully:

• libsForQt5.kimageformats (libsForQt515.kimageformats ,plasma5Packages.kimageformats)
• libsForQt514.kimageformats
• photoqt

Note that build failures may predate this PR, and could be nondeterministic or hardware dependent.
Please exercise your independent judgement. Does something look off? Please file an issue or reach out on IRC.

---

Result of nixpkgs-review pr 127862 at 69d9445 run on x86_64-linux 1

1 package failed to build:

• libsForQt512.kimageformats

3 packages built successfully:

• libsForQt5.kimageformats (libsForQt515.kimageformats ,plasma5Packages.kimageformats)
• libsForQt514.kimageformats
• photoqt

Note that build failures may predate this PR, and could be nondeterministic or hardware dependent.
Please exercise your independent judgement. Does something look off? Please file an issue or reach out on IRC.