This merges all the files for main.py together again except
generator_lib.py because there doesn't seeem to be a good way to
separate the pure dawn.json generators and the dawn wire generator.
Also updates the GN templates to make it easier to define new generators
based on generator_lib, and move the Jinja2 template "stdlib" to
generator_lib.py
BUG=dawn:165
Change-Id: I1b5b2ef0a59cb142e214f3af9a58048a88ae949a
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/7880
Commit-Queue: Kai Ninomiya <kainino@chromium.org>
Reviewed-by: Austin Eng <enga@chromium.org>
Reviewed-by: Kai Ninomiya <kainino@chromium.org>
Corentin Wallez