Add layout(marker) to SkSL

Allows for uniforms to be automatically populated with
marked canvas matrices:

SkSL:
  layout (marker=localToWorld) uniform float4x4 localToWorldMatrix;

C++:
  canvas->concat(...);
  canvas->markCTM("localToWorld");
  canvas->concat(...);
  canvas->drawFoo(...);

Any runtime effects created with that SkSL will have their
localToWorldMatrix uniform filled in with the CTM, ignoring
any transformation that happened before/above the markCTM
call. The marker needs to be a sequence of alphanumeric or
underscore characters, and match the string used in markCTM.

The marker can also be of the form "normals(<string>)", in
which case the uniform will be filled in with the transpose
of the inverse of the upper-left 3x3 portion of the CTM
identified by <string>. This is helpful for transforming
normal vectors, as is often done in lighting.

Change-Id: I7d1ca4dc3f8fabbe91b9bd2c8632013f26d2321a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/285376
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
8 files changed