Add unit test demonstrating structs in a module.

The generated code is not yet correct; the struct from the module is
not incorporated into the final output.

Change-Id: Ib9a689237be69d9a80087202240f007cacfc2d41
Bug: b/320462028
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/805497
Commit-Queue: Brian Osman <brianosman@google.com>
Auto-Submit: John Stiles <johnstiles@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: John Stiles <johnstiles@google.com>
22 files changed