use simplier validation to include form attribute

Author: jupapios

packages/react-dom-bindings/src/events/plugins/FormActionEventPlugin.js

@@ -92,8 +92,7 @@ function extractEvents(
       const temp = submitter.ownerDocument.createElement('input');
       temp.name = submitter.name;
       temp.value = submitter.value;
-      const isOutsideForm = !form.contains(submitter);
-      if (isOutsideForm) {
+      if (form.id) {
         temp.setAttribute('form', form.id);
       }
       (submitter.parentNode: any).insertBefore(temp, submitter);

packages/react-dom/src/__tests__/ReactDOMForm-test.js

@@ -494,21 +494,24 @@ describe('ReactDOMForm', () => {
     await act(async () => {
       root.render(
         <>
-          <button
-            form="form"
-            name="button"
-            value="outside"
-            ref={outsideButtonRef}>
-            Edit from outside
-          </button>
-          <form id="form" action={action}>
+          <form action={action}>
             <input type="text" name="title" defaultValue="hello" />
             <input type="submit" name="button" value="save" />
             <input type="submit" name="button" value="delete" ref={inputRef} />
             <button name="button" value="edit" ref={buttonRef}>
               Edit
             </button>
           </form>
+          <form id="form" action={action}>
+            <input type="text" name="title" defaultValue="hello" />
+          </form>
+          <button
+            form="form"
+            name="button"
+            value="outside"
+            ref={outsideButtonRef}>
+            Button outside form
+          </button>
           ,
         </>,
       );