Particles + Interpreter: Bind particle's SkRandom to "rand"

Update sample effects to use that (and remove the need for the
hacky workaround "random -> frame" affector I was using).

Current perf on my workstation, 6k particles updating:
native: 0.67 ms
interp: 0.97 ms

Change-Id: I3a2168c210d7431ffffe2b87ab6adade69f1dce7
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/214190
Reviewed-by: Ethan Nicholas <ethannicholas@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
2 files changed