refactor(core): change module semantics

This contains major changes to the compiler, bootstrap of the platforms
and test environment initialization.

Main part of #10043
Closes #10164

BREAKING CHANGE:
- Semantics and name of `@AppModule` (now `@NgModule`) changed quite a bit.
  This is actually not breaking as `@AppModules` were not part of rc.4.
  We will have detailed docs on `@NgModule` separately.
- `coreLoadAndBootstrap` and `coreBootstrap` can't be used any more (without migration support).
  Use `bootstrapModule` / `bootstrapModuleFactory` instead.
- All Components listed in routes have to be part of the `declarations` of an NgModule.
  Either directly on the bootstrap module / lazy loaded module, or in an NgModule imported by them.

tools/public_api_guard/platform-browser/testing.d.ts

@@ -1,12 +1,12 @@
-/** @stable */
-export declare class BrowserTestModule {
+/** @experimental */
+export declare class BrowserTestingModule {
 }
 
 /** @experimental */
-export declare const browserTestPlatform: () => PlatformRef;
+export declare const browserTestingPlatform: (extraProviders?: any[]) => PlatformRef;
 
 /** @deprecated */
 export declare const TEST_BROWSER_APPLICATION_PROVIDERS: Array<any>;
 
-/** @experimental */
+/** @deprecated */
 export declare const TEST_BROWSER_PLATFORM_PROVIDERS: Array<any>;