Modify GrGLSLGP's logic to add a varying for a series of matrix sample
usages below a DeviceSpace FP in the FP hierarchy. The varying is based
off the GPs position output variable in the VS.
Adds a new sample usage type for the DeviceSpace FP.
Bug: skia:12198
Change-Id: Ic39f3296c60a073656ad0c72a431a462d5714e92
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/435717
Commit-Queue: Brian Salomon <bsalomon@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Reviewed-by: Michael Ludwig <michaelludwig@google.com>
9eca2ca0c6