feat(bazel): change ng_package rule to APF v6 (#22782)

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

packages/platform-browser/testing/BUILD.bazel

@@ -1,5 +1,7 @@
 package(default_visibility = ["//visibility:public"])
 
+exports_files(["package.json"])
+
 load("//tools:defaults.bzl", "ng_module")
 
 ng_module(