Fixes to array handling and interface blocks

- Use a named constant for unsized array columns. Some places were using
  0, others were using -1. (It's now -1 everywhere).
- Fix dehydrate/rehydrate of unsized arrays.
- Change sk_in to be an unsized array - this matches the GLSL
  declaration (the size is implicitly the number of vertices per
  primitive). It also makes our use of sk_in where we index it not look
  like out-of-bounds access.

Change-Id: I64b9e81872ed71bcb691657d21b5713217b0b5e9
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/321553
Reviewed-by: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
9 files changed