Animations

[0HyperCube]

Since there was no issue open
Previously discussed in #1601.
A partial implementation in #1766.
Set as a Google Summer of Code: https://graphite.rs/volunteer/guide/student-projects/#animation-system

This work was stalled because of the constant folding: non-async secondary inputs are all evaluated as the graph is compiled.

Possible solutions:

• All nodes are async (no constant folding)
• Somehow determine if nodes are actually constants.
• Just recompile the graph each frame (as proposed by TrueDoctor in discord)

  For the animation we will need to rely on sufficiently fast compilation speeds. Incremental compilation will help as well in that regard.

Concept by Keavon