loader: Add support for gif

[BenjaminHalko]

Adds support for loading the .gif format in picture. You can use animation to animate it as well.

It also supports using giflib as an external library

issue: https://github.com/thorvg/thorvg/issues/3453

[hermet]

@BenjaminHalko Thanks, Could you please resolve the copilot comments? (you can close them if they are false-alarm)

[BenjaminHalko]

@hermet OK, I think all the issues have been fixed 👍

[hermet]

feature target: thorvg v2.0