Textarea: Add "title" to story example (#4983)

* Add "title" to form example

* Add caption to explain purpose

* test(vrt): update snapshots

---------

Co-authored-by: TylerJDev <[email protected]>

Author: TylerJDev

.playwright/snapshots/components/Textarea.test.ts-snapshots/Textarea-Visually-Hidden-Label-dark-colorblind-linux.png

@@ -1,5 +1,5 @@
 import React from 'react'
-import {Box, FormControl} from '..'
+import {Box, FormControl, Heading} from '..'
 import Textarea from '../Textarea'
 
 export default {
@@ -27,9 +27,13 @@ export const WithCaption = () => (
 
 export const VisuallyHiddenLabel = () => (
   <Box as="form">
+    <Heading as="h2" variant="small">
+      Primer form title
+    </Heading>
     <FormControl>
-      <FormControl.Label visuallyHidden>Default label</FormControl.Label>
+      <FormControl.Label visuallyHidden>Primer form label</FormControl.Label>
       <Textarea />
+      <FormControl.Caption>Label is visually hidden; the title describes the purpose visually</FormControl.Caption>
     </FormControl>
   </Box>
 )