feat(forms): add option to use browser's native validation and angular forms (#13566)

Also renames NgNovalidate -> NgNoValidate

Closes #13573

modules/@angular/forms/test/template_integration_spec.ts

@@ -97,6 +97,16 @@ export function main() {
            expect(form.nativeElement.getAttribute('novalidate')).toEqual('');
          }));
 
+      it('should be possible to use native validation and angular forms', fakeAsync(() => {
+           const fixture = initTest(NgModelNativeValidateForm);
+
+           fixture.detectChanges();
+           tick();
+
+           const form = fixture.debugElement.query(By.css('form'));
+           expect(form.nativeElement.hasAttribute('novalidate')).toEqual(false);
+         }));
+
       it('should support ngModelGroup', fakeAsync(() => {
            const fixture = initTest(NgModelGroupForm);
            fixture.componentInstance.first = 'Nancy';
@@ -258,7 +268,7 @@ export function main() {
         const fixture = initTest(NgNoFormComp);
         fixture.detectChanges();
         const form = fixture.debugElement.query(By.css('form'));
-        expect(form.nativeElement.hasAttribute('novalidate')).toBeFalsy();
+        expect(form.nativeElement.hasAttribute('novalidate')).toEqual(false);
       });
     });
 
@@ -1222,6 +1232,10 @@ class NgModelForm {
   onReset() {}
 }
 
+@Component({selector: 'ng-model-native-validate-form', template: `<form ngNativeValidate></form>`})
+class NgModelNativeValidateForm {
+}
+
 @Component({
   selector: 'ng-model-group-form',
   template: `