Add support for .js based plugins, custom plugin_name to prevent
conflicts with server-side plugins with the same name.
Here's an example:
https://chromium-review.googlesource.com/c/infra/gerrit-plugins/landingwidget/+/1295049
So what we want to achieve is to have:
gerrit_plugin(
name = "landingwidget",
[...]
and
polygerrit_plugin(
name = "landingwidget_ui",
plugin_name = "landingwidget",
[...]
and produce the following final artifacts:
landingwidget.jar
landingwidget.js
Change-Id: Ic9c68809cbaaf4650301d98e56d7c1c76e008251
3c1139ee68