fix(testing): add an explicit doAsyncPrecompilation step (#10015)

This removes the magic from the `inject` test helper that would inspect
the current zone and would only work with our `async` test helper.
Now, `inject` is always synchronous, and if you are using a module
that requires async precompilation, you're required to call
`doAsyncPrecompilation` in your tests.

This is part of the breaking changes introduced with the swap
to each test having an AppModule.

Closes #9975
Closes #9593

BREAKING CHANGE:

`TestInjector` is now renamed to `TestBed`

Before:

```js
import {TestInjector, getTestInjector} from '@angular/core/testing';
```

After:

```js
import {TestBed, getTestBed} from '@angular/core/testing';
```

modules/@angular/compiler/testing/test_component_builder.ts

@@ -7,12 +7,13 @@
  */
 
 import {AnimationEntryMetadata, Compiler, ComponentFactory, Inject, Injectable, Injector, NgZone, ViewMetadata} from '@angular/core';
-import {ComponentFixture, ComponentFixtureNoNgZone, TestComponentBuilder, TestInjector} from '@angular/core/testing';
+import {ComponentFixture, ComponentFixtureNoNgZone, TestBed, TestComponentBuilder} from '@angular/core/testing';
 
 import {DirectiveResolver, ViewResolver} from '../index';
 import {MapWrapper} from '../src/facade/collection';
 import {ConcreteType, IS_DART, Type, isPresent} from '../src/facade/lang';
 
+
 /**
  * A TestComponentBuilder that allows overriding based on the compiler.
  */
@@ -31,7 +32,7 @@ export class OverridingTestComponentBuilder extends TestComponentBuilder {
   /** @internal */
   _viewOverrides = new Map<Type, ViewMetadata>();
 
-  constructor(@Inject(TestInjector) injector: Injector) { super(injector); }
+  constructor(@Inject(TestBed) injector: Injector) { super(injector); }
 
   /** @internal */
   _clone(): OverridingTestComponentBuilder {