Improved Gifs

[EricBAndrews]

Issues

• closes Better webp, gif rendering #1883

Description

• Improves scrubbing performance for gifs and webps. Scrubbing backwards on large gifs is now nice and smooth (https://sh.itjust.works/post/33262204 being a nice testing image)
• Adds time markers to playback bar

Implementation Notes

• Rewrites AnimatedImageView as a UIViewRepresentable around SDAnimatedImageView. This gives us access to SDAnimatedImage.preloadAllFrames(), loads the entire gif into memory and thus enables smooth backwards scrubbing. It also simplifies a lot of the logic around interacting with the AnimatedImageView.
• Updates how AnimatedImageView populates controlState.playbackPosition; there is now an observer on the SDAnimatedImagePlayer that listens to frame changes.
• Adds scrubbingAvailable to MediaControlState. This lets us only perform preloadAllFrames when we actually need to.
• Adds duration to MediaControlState

[Sjmarf]

Nice, this is super smooth! One minor implementation question