Runtime Effects: Support 'uniform shader' (vs. 'in shader')

The previous behavior leaked Skia-internal concepts into public SkSL.
Users coming from GLSL will expect that bindable/sampleable objects are
uniform (just like texture2D). This keeps the old support around (and
tested), but updates all of our examples to use 'uniform'.

Bug: skia:10679
Change-Id: I0c98162f5e21dad7014d9778ceb26143d2f6030e
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/332376
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: John Stiles <johnstiles@google.com>
17 files changed