refactor(core): clean up platform bootstrap and initTestEnvironment

- Introduces `CompilerFactory` which can be part of a `PlatformRef`.
- Introduces `WorkerAppModule`, `WorkerUiModule`, `ServerModule`
- Introduces `serverDynamicPlatform` for applications using runtime compilation
  on the server.
- Changes browser bootstrap for runtime and offline compilation (see below for an example).
  * introduces `bootstrapModule` and `bootstrapModuleFactory` in `@angular/core`
  * introduces new `browserDynamicPlatform` in `@angular/platform-browser-dynamic
- Changes `initTestEnvironment` (which used to be `setBaseTestProviders`) to not take a compiler factory any more (see below for an example).

BREAKING CHANGE:

## Migration from `setBaseTestProviders` to `initTestEnvironment`:

- For the browser platform:
  BEFORE:
  ```
  import {setBaseTestProviders} from ‘@angular/core/testing’;
  import {TEST_BROWSER_DYNAMIC_PLATFORM_PROVIDERS,
      TEST_BROWSER_DYNAMIC_APPLICATION_PROVIDERS} from ‘@angular/platform-browser-dynamic/testing’;

  setBaseTestProviders(TEST_BROWSER_DYNAMIC_PLATFORM_PROVIDERS,
      TEST_BROWSER_DYNAMIC_APPLICATION_PROVIDERS);
  ```

  AFTER:
  ```
  import {initTestEnvironment} from ‘@angular/core/testing’;
  import {browserDynamicTestPlatform,
      BrowserDynamicTestModule} from ‘@angular/platform-browser-dynamic/testing’;

  initTestEnvironment(
      BrowserDynamicTestModule,
      browserDynamicTestPlatform());

  ```
- For the server platform:
  BEFORE:
  ```
  import {setBaseTestProviders} from ‘@angular/core/testing’;
  import {TEST_SERVER_PLATFORM_PROVIDERS,
      TEST_SERVER_APPLICATION_PROVIDERS} from ‘@angular/platform-server/testing/server’;

  setBaseTestProviders(TEST_SERVER_PLATFORM_PROVIDERS,
      TEST_SERVER_APPLICATION_PROVIDERS);
  ```

  AFTER:
  ```
  import {initTestEnvironment} from ‘@angular/core/testing’;
  import {serverTestPlatform,
      ServerTestModule} from ‘@angular/platform-browser-dynamic/testing’;

  initTestEnvironment(
      ServerTestModule,
      serverTestPlatform());

  ```

## Bootstrap changes
```
@AppModule({
  modules: [BrowserModule],
  precompile: [MainComponent],
  providers: […], // additional providers
  directives: […], // additional platform directives
  pipes: […] // additional platform pipes
})
class MyModule {
  constructor(appRef: ApplicationRef) {
    appRef.bootstrap(MainComponent);
  }
}

// offline compile
import {browserPlatform} from ‘@angular/platform-browser’;
import {bootstrapModuleFactory} from ‘@angular/core’;

bootstrapModuleFactory(MyModuleNgFactory, browserPlatform());

// runtime compile long form
import {browserDynamicPlatform} from ‘@angular/platform-browser-dynamic’;
import {bootstrapModule} from ‘@angular/core’;

bootstrapModule(MyModule, browserDynamicPlatform());
```

Closes #9922
Part of #9726

tools/public_api_guard/core/index.d.ts

@@ -256,6 +256,12 @@ export declare class Binding extends Provider {
     });
 }
 
+/** @stable */
+export declare function bootstrapModule<M>(moduleType: ConcreteType<M>, platform: PlatformRef, compilerOptions?: CompilerOptions): Promise<AppModuleRef<M>>;
+
+/** @experimental */
+export declare function bootstrapModuleFactory<M>(moduleFactory: AppModuleFactory<M>, platform: PlatformRef): AppModuleRef<M>;
+
 /** @stable */
 export declare enum ChangeDetectionStrategy {
     OnPush = 0,
@@ -302,6 +308,22 @@ export declare class Compiler {
     compileComponentSync<T>(component: ConcreteType<T>): ComponentFactory<T>;
 }
 
+/** @experimental */
+export declare abstract class CompilerFactory {
+    abstract createCompiler(options?: CompilerOptions): Compiler;
+    withDefaults(options?: CompilerOptions): CompilerFactory;
+    static mergeOptions(defaultOptions?: CompilerOptions, newOptions?: CompilerOptions): CompilerOptions;
+}
+
+/** @experimental */
+export declare type CompilerOptions = {
+    useDebug?: boolean;
+    useJit?: boolean;
+    defaultEncapsulation?: ViewEncapsulation;
+    providers?: any[];
+    deprecatedAppProviders?: any[];
+};
+
 /** @stable */
 export declare var Component: ComponentMetadataFactory;
 
@@ -513,6 +535,9 @@ export declare function coreLoadAndBootstrap(componentType: Type, injector: Inje
 /** @experimental */
 export declare function createPlatform(injector: Injector): PlatformRef;
 
+/** @experimental */
+export declare function createPlatformFactory(name: string, providers: any[]): () => PlatformRef;
+
 /** @stable */
 export declare class CyclicDependencyError extends AbstractProviderError {
     constructor(injector: ReflectiveInjector, key: ReflectiveKey);