Change how vertex/instance attributes are handled in geometry processors.

* No longer register vertex/instance attributes on base class, just counts

* Separate instance and vertex attributes and remove InputRate and offset

* Make attributes constexpr where possible

Change-Id: I1f1d5e772fa177a96d2aeb805aab7b69f35bfae6
Reviewed-on: https://skia-review.googlesource.com/132405
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Chris Dalton <csmartdalton@google.com>
54 files changed