Use frontend-shared components in CreateGroupForm

Use components from our component library (specifically `<Input>`,
`<Textarea>` and `<Button>`) in the `<CreateGroupForm>`.

Instead of using the HTML from h's legacy forms. This legacy HTML
doesn't work anymore anyway because the CSS it depends on is now
isolated from the Preact app by shadow DOM.

h/static/scripts/group-forms/components/CreateGroupForm.tsx

@@ -1,36 +1,29 @@
+import { Button, Input, Textarea } from '@hypothesis/frontend-shared';
+
 export default function CreateGroupForm() {
   return (
     <>
       <h1>Create a new private group</h1>
 
       <form>
         <div>
-          <label for="name">
-            Name <span>*</span>
-          </label>
-          <input type="text" id="name" autofocus autocomplete="off" required />
-          <span>0/25</span>
+          <label for="name">Name*</label>
+          <Input id="name" autofocus autocomplete="off" required />
+          0/25
         </div>
 
         <div>
           <label for="description">Description</label>
-          <textarea id="description"></textarea>
-          <span>0/250</span>
+          <Textarea id="description" />
+          0/250
         </div>
 
         <div>
-          <div>
-            <button>Create group</button>
-          </div>
+          <Button variant="primary">Create group</Button>
         </div>
       </form>
 
-      <footer>
-        <span>
-          <span>*</span>
-          <span>Required</span>
-        </span>
-      </footer>
+      <footer>*Required</footer>
     </>
   );
 }