Fix WGSL global-variable initialization.

The WGSL code generator was neglecting the initial-value and `const`
modifier on global variables. Const-global variables are now declared
as `const` and initial-values are properly assigned.

Change-Id: I7b861b75f5e94d38f9395369709deeb5eebedbbe
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/706977
Commit-Queue: Arman Uguray <armansito@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Arman Uguray <armansito@google.com>
2 files changed