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/src/schema/dom_element_schema_registry.ts

@@ -313,4 +313,6 @@ export class DomElementSchemaRegistry extends ElementSchemaRegistry {
     var mappedPropName = StringMapWrapper.get(attrToPropMap, propName);
     return isPresent(mappedPropName) ? mappedPropName : propName;
   }
+
+  getDefaultComponentElementName(): string { return 'ng-component'; }
 }