Update deprecated ShaderModuleWGSLDescriptor.source to .code instead.

Change-Id: Iaee67ad7c5a3e761f9b49eeccb0cef245edbb730
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/687196
Commit-Queue: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Jim Van Verth <jvanverth@google.com>
Auto-Submit: Loko Kung <lokokung@google.com>
2 files changed