Fixed some GrSkSLFP limitations.

This makes it possible to pass more types as uniforms / inputs and fixes an
issue with non-main functions calling other non-main functions.

Change-Id: I6b5623b3c967d8219b992a455cc68bb0a29706b8
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/255300
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Ethan Nicholas <ethannicholas@google.com>
4 files changed