build: publish tree of files rather than FESMs (#18541)

* Remove now unnecessary portions of build.
* Add a compilePackageES5 method to build ES5 from sources
* Rework all package.json and rollup config files to new format
* Remove "extends" from tsconfig-build.json files and fixup compilation roots

PR Close #18541

packages/platform-browser/testing/rollup.config.js

@@ -7,6 +7,7 @@
  */
 
 import resolve from 'rollup-plugin-node-resolve';
+import sourcemaps from 'rollup-plugin-sourcemaps';
 
 const globals = {
   '@angular/core': 'ng.core',
@@ -15,12 +16,12 @@ const globals = {
 };
 
 export default {
-  entry: '../../../dist/packages-dist/platform-browser/@angular/platform-browser/testing.es5.js',
+  entry: '../../../dist/packages-dist/platform-browser/esm5/testing/index.js',
   dest: '../../../dist/packages-dist/platform-browser/bundles/platform-browser-testing.umd.js',
   format: 'umd',
   exports: 'named',
   moduleName: 'ng.platformBrowser.testing',
-  plugins: [resolve()],
+  plugins: [resolve(), sourcemaps()],
   external: Object.keys(globals),
   globals: globals
 };