fix(core): support components without a selector (#10331)

Components without a selector now get the selector `ng-component`.
Directives without a selector will throw an error message.

Closes #3464
Closes #10216

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

@@ -29,4 +29,6 @@ export class MockSchemaRegistry implements ElementSchemaRegistry {
     var result = this.attrPropMapping[attrName];
     return isPresent(result) ? result : attrName;
   }
+
+  getDefaultComponentElementName(): string { return 'ng-component'; }
 }