Changes the name of generated rules to be valid in more cases

[mattnathan]

In addition if you are outputting the generated files into a folder that looks like the npm package name then omit the prefix part to simplify importing in bazel.

For example if you npm package is @vue/cli and your output dir is ~/myrepo/vue/cli then the generated rule name will now be cli which will allow importing like //myrepo/vue/cli. If the output dir doesn't match the package name then any / will be replaced by '_' in the rule name.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}