feat(bazel): add an ng_package rule (#22221)

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

packages/core/testing/BUILD.bazel

@@ -4,10 +4,17 @@ load("//tools:defaults.bzl", "ng_module")
 
 ng_module(
     name = "testing",
-    srcs = glob(["**/*.ts"]),
+    srcs = glob(
+        ["**/*.ts"],
+    ),
     module_name = "@angular/core/testing",
     deps = [
         "//packages:types",
         "//packages/core",
     ],
 )
+
+filegroup(
+    name = "npm_package_assets",
+    srcs = ["package.json"],
+)