fix(core/testing compiler/testing): move TestComponentBuilder to core/testing (#9590)

TestComponentBuilder now lives in core/testing. compiler/testing contains a private
OverridingTestComponentBuilder implementation which handles the private behavior
we need to override templates. This is part of the effort to simplify the testing
imports and hide compiler APIs.

Closes #9585

BREAKING CHANGE:

`TestComponentBuilder` is now imported from `@angular/core/testing`. Imports
from `@angular/compiler/testing` are deprecated.

Before:

```
import {TestComponentBuilder, TestComponentRenderer, ComponentFixtureAutoDetect} from '@angular/compiler/testing';
```

After:
```
import {TestComponentBuilder, TestComponentRenderer, ComponentFixtureAutoDetect} from '@angular/core/testing';
```

modules/@angular/core/testing.ts

@@ -9,5 +9,6 @@
 export * from './testing/async';
 export * from './testing/component_fixture';
 export * from './testing/fake_async';
+export * from './testing/test_component_builder';
 export * from './testing/test_injector';
 export * from './testing/testing';