Support animated media thumbnails (MSC2705)

Since 2020, Animated Media Thumbnails have been possible in Matrix through MSC2705. Being an MSC it didn't see wide adoption.

Since April 1st (no, not a joke) of this year, animated media thumbnails are officially a part of the Matrix Specification, and are soon going to become a part of Matrix 1.11.

It would be really nice if Fractal were to support this already, as it would spell the first client to do so and allows users to have e.g animated avatars whilst preserving the requested image size.

Some things to keep in mind:

• #960 - There was supposed to be discussion here about handling GIFs and animated media in general.

  • Also related: Accessibility.

• I've made sure to do a quick check to see whether a related issue already exists.