Angular Package Format v6 stops bundling files in the esm5 and esm2015
directories, now that Webpack 4 can tree-shake per-file.
Adds some missing files like package.json to make packages closer to
what we publish today.
Refactor ng_package to be a type of npm_package and re-use the packaging
action from that rule.
PR Close#22782
This produces a directory following the Angular Package layout spec.
Includes integration test coverage by making a minimal ng_package in integration/bazel.
Unit tests verify the content of the @angular/core and @angular/common packages.
This doesn't totally match our current output, but is good enough to unblock some
early adopters.
It re-uses logic from the rollup_bundle rule in rules_nodejs. It should also
eventually have the .pack and .publish secondary targets like npm_package rule.
PR Close#22221
