Reland "Revert "New approach to GrProcessor uniforms.""

This reverts commit a59925fb1dfaddff6add72929bfa882fc72d5cc3.

Reason for revert: Speculative revert for https://crbug.com/1251070

Original change's description:
> Revert "Revert "New approach to GrProcessor uniforms.""
>
> This reverts commit ae59426ea6e9b351d9d52f2a9c12d05023351994.
>
> Bug: skia:12182
> Change-Id: I591a0a89ffad1a3d5d867dd247ceeec71b6041a4
> Reviewed-on: https://skia-review.googlesource.com/c/skia/+/449516
> Reviewed-by: Michael Ludwig <michaelludwig@google.com>
> Commit-Queue: Brian Salomon <bsalomon@google.com>

Bug: skia:12182
Change-Id: I2f37c7e9675dd35194791340012e1b4135b076a1
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/450440
Bot-Commit: Rubber Stamper <rubber-stamper@appspot.gserviceaccount.com>
Commit-Queue: Jim Van Verth <jvanverth@google.com>
52 files changed