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.

modules/@angular/common/index.ts

@@ -6,9 +6,25 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
+import {NgModule} from '@angular/core';
+import {COMMON_DIRECTIVES} from './src/common_directives';
+import {COMMON_PIPES} from './src/pipes';
+
 export * from './src/pipes';
 export * from './src/directives';
 export * from './src/forms-deprecated';
 export * from './src/common_directives';
 export * from './src/location';
-export {NgLocalization} from './src/localization';
+export {NgLocalization} from './src/localization';
+
+// Note: This does not contain the location providers,
+// as they need some platform specific implementations to work.
+/**
+ * The module that includes all the basic Angular directives like {@link NgIf}, ${link NgFor}, ...
+ *
+ * @experimental
+ */
+@NgModule(
+    {declarations: [COMMON_DIRECTIVES, COMMON_PIPES], exports: [COMMON_DIRECTIVES, COMMON_PIPES]})
+export class CommonModule {
+}