[graphite][compute] Remove draw-specific parameters

Removed parameters related to Graphite's draw system (DrawParams,
ssboIndex, etc) from the ComputeStep interface and
DispatchGroup::Builder. While draws will take advantage of ComputeSteps
for geomtery and image processing in the future, having these data
structures exposed at this level made the interface awkward in cases
that don't directly integrate with the draw system (e.g. vello shaders,
or ad hoc image filters) which had to use placeholder instances just to
satisfy the contract.

The plan going forward is to define specialized interfaces that are
layered on top of DispatchGroup and ComputeStep based on the use case.
The rough outline for the goals here are described in b/279955342.

Bug: b/279955342
Change-Id: I75f12a7e70367ed44af2f29ed8684130c3597ac4
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/736297
Commit-Queue: Arman Uguray <armansito@google.com>
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
8 files changed