build: introduce a package.bzl (#26488)

This lets Angular Bazel users install our transitive deps, rather than have to list them in their WORKSPACE file.
If they want a different version of one of these deps, they just need to install it before calling rules_angular_dependencies.

PR Close #26488

packages/bazel/BUILD.bazel

@@ -8,9 +8,8 @@ genrule(
 
 npm_package(
     name = "npm_package",
-    srcs = [
+    srcs = glob(["*.bzl"]) + [
         "BUILD.bazel",
-        "index.bzl",
         "package.json",
         "//packages/bazel/src:package_assets",
     ],