Disallow opaque types in structs and interface blocks.

This is a followup to http://review.skia.org/335196. This detects opaque
types (samplers and textures) at parsing or IR generation time and
reports an error regardless of backend. This check occurs before Metal
or SPIR-V would have a chance to detect the error, so it changes their
output to a slightly more focused error message. The Metal/SPIR-V fix in
the prior CL is still a nice broad catch-all for preventing spurious
ABORTs, though.

Change-Id: I4cce92a8767d72b5d3d7277a8afde8ce5ce86db2
Bug: skia:10956
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/335217
Commit-Queue: John Stiles <johnstiles@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
11 files changed