Particles: Removed emitters, added more full-featured position affectors

Bug: skia:
Change-Id: Ie6485a11bb57fecef470d727dcf3b4fe5dff0b90
Reviewed-on: https://skia-review.googlesource.com/c/195582
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
7 files changed