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/compiler-cli/README.md

@@ -30,13 +30,14 @@ generated code:
 main_module.ts
 -------------
 import {BrowserModule} from '@angular/platform-browser';
-import {Component, AppModule, ApplicationRef} from '@angular/core';
+import {Component, NgModule, ApplicationRef} from '@angular/core';
 
 @Component(...)
 export class MyComponent {}
 
-@AppModule({
-  modules: [BrowserModule],
+@NgModule({
+  imports: [BrowserModule],
+  declarations: [MyComponent],
   precompile: [MyComponent]
 })
 export class MainModule {