build: expose flatModuleOutFile option on ng_module (#22814)

This lets projects like Material change ng_package "bundle index" files to non-conflicting paths

Currently packages like @angular/core ship with the generated metadata
in a path like 'core.js' which overwrites one of the inputs.

Angular material puts the generated file in a path like 'index.js'

Either way these files generated by ng_module rules have the potential
to collide with inputs given by the user, which results in an error.

Instead, give users the freedom to choose a different non-conflicting name.

Also this refactors the ng_package rule, removing the redundant
secondary_entry_points attribute.

Instead, we assume that any ng_module in the deps with a module_name
attribute is a secondary entry point.

PR Close #22814

packages/compiler-cli/integrationtest/bazel/ng_module/BUILD.bazel

@@ -4,6 +4,7 @@ ng_module(
     name = "test_module",
     srcs = glob(["*.ts"]),
     entry_point = "index.ts",
+    flat_module_out_file = "flat_module_filename",
     module_name = "some_npm_module",
     deps = ["//packages/core"],
 )

packages/compiler-cli/integrationtest/bazel/ng_module/extract_flat_module_index.bzl

@@ -6,11 +6,12 @@
 """
 
 def _extract_flat_module_index(ctx):
-  return [DefaultInfo(files = depset(transitive = [
-      dep.angular.flat_module_metadata
-      for dep in ctx.attr.deps
-      if hasattr(dep, "angular")
-  ]))]
+  files = []
+  for dep in ctx.attr.deps:
+    if hasattr(dep, "angular"):
+      for metadata in dep.angular.flat_module_metadata:
+        files.extend([metadata.metadata_file, metadata.typings_file])
+  return [DefaultInfo(files = depset(files))]
 
 extract_flat_module_index = rule(
     implementation = _extract_flat_module_index,

packages/compiler-cli/integrationtest/bazel/ng_module/spec.js

@@ -12,7 +12,7 @@ describe('flat module index', () => {
   describe('child metadata', () => {
     it('should have contents', () => {
       const metadata = fs.readFileSync(
-          require.resolve(`${PKG}/_test_module.bundle_index.metadata.json`), {encoding: 'utf-8'});
+          require.resolve(`${PKG}/flat_module_filename.metadata.json`), {encoding: 'utf-8'});
       expect(metadata).toContain('"__symbolic":"module"');
       expect(metadata).toContain('"__symbolic":"reference","module":"@angular/core"');
       expect(metadata).toContain('"origins":{"Child":"./child","ɵa":"./parent"}');
@@ -21,8 +21,8 @@ describe('flat module index', () => {
   });
   describe('child typings', () => {
     it('should have contents', () => {
-      const dts = fs.readFileSync(
-          require.resolve(`${PKG}/_test_module.bundle_index.d.ts`), {encoding: 'utf-8'});
+      const dts =
+          fs.readFileSync(require.resolve(`${PKG}/flat_module_filename.d.ts`), {encoding: 'utf-8'});
 
       expect(dts).toContain('export * from \'./index\';');
       expect(dts).toContain('export { Parent as ɵa } from \'./parent\';');