Patch Support For write_source_files

It would be nice to have the capability of providing a list of patches to the write_source_files rule. I know you can apply patches at the http_archive / git_archive level, but sometimes you need different patches for each destination.

As a feature request, it would be nice for the `write_source_files` rule to support `patch` and `patch_args` mechanisms, just like the http_archive rule.

Thank you!

Start by locating the write_source_files rule and compare its behavior with the patch and patch_args mechanisms in http_archive and git_archive. Determine how patches should differ for each destination, then verify that per-destination patches and patch arguments work as requested.

Written by the indexing model from the issue text.