[dolphin] Animate gifs on preview
Adds the capability to view animated images on the preview in the information panel.
This was a request from a user back in 2009 (https://bugs.kde.org/show_bug.cgi?id=182257), but I think nowadays with stickers/memes and what not, it's even more useful.
It keeps the size default transition of the preview viewer before starting the animation, so that the visual integration is smoother.
Test Plan: Open the information panel and hover over some animated images (gif/webp/mng)
Reviewed By: VDG, ngraham
Subscribers: pino, fuksitter, meven, broulik, kfm-devel
Differential Revision: https://phabricator.kde.org/D23538