Fix fuzzer-discovered assertion with WGSL interface-block arrays.

These are not supported; previously, we would assert while
attempting to emit code for them. Now, we report an error.

Bug: oss-fuzz:63353
Change-Id: I2d644cd616ca2c97ed1d69f4fb02ba5971a63e63
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/768874
Reviewed-by: Nicolette Prevost <nicolettep@google.com>
Commit-Queue: Nicolette Prevost <nicolettep@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
16 files changed