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/animations/browser/index.ts

@@ -11,4 +11,4 @@
 // replaces this file with production index.ts when it rewrites private symbol
 // names.
 
-export * from './src/browser';
+export * from './public_api';