Render loop optimizations

[wouterlucas]

We've spent a few rounds of doing render loop optimizations and discovered there are several improvements that can be made. Consider this round # 1 of our performance hunt.

Current list of changes:

• Pause RAF when there are no updates
• Do not render if there are no tree updates
• Animation loop code optimizations
• Change node sorting to presorting
• Disable Batched Shader for now, due to branching issues
• Excessive texture rebinds per draw

Benchmarking
We've used two benchmarking methods:

• Blits 1080p stress test of a continuous animation with 103 images
• Simple 720p animation on L2 and L3

Observations, all tested on a RPI3 with WPEWebKit 2.42:
Simple animation on L2 @ 720p rendered at ~59 FPS
Simple animation on L3 @ 720p rendered at 33 FPS at the start of this exercise
Simple animation on L3 @ 720p renders at 47 FPS with the above changes, excluding texture rebinds
Simple animation on L3 @ 720p renders at ~59 FPS

Blits stress test @ 1080p renders at 12 FPS prior to these changes
Blits stress test @ 1080p renders at 27 FPS with the above changes excluding texture rebinds
Blits stress test @ 1080p renders at 47 FPS with a texture rebind hack (TODO implementation).
Blits stress test @ 1080p renders at 31 FPS with changes

@erikhaandrikman for all the support & hunting 🤟

Todo:

• Come up with a way to handle texture rebinds
• Run visual regression testing

[CLAassistant]

All committers have signed the CLA.