These async methods are a replacement for the Observable based `runSchematicAsync` and `runExternalSchematicAsync` methods.
DEPRECATED:
The Observable based `SchematicTestRunner.runSchematicAsync` and `SchematicTestRunner.runExternalSchematicAsync` method have been deprecated in favor of the Promise based `SchematicTestRunner.runSchematic` and `SchematicTestRunner.runExternalSchematic`.
This commit adds an internal file to export needed symbols from `@angular/platform-server` when building a server bundle. This is needed. This is needed so that DI tokens can be referenced and set at runtime outside of the bundle.
Also, it adds a migration to remove these exports from the users files as otherwise an export collision would occur due to the same symbol being exported multiple times.
