docs: add getDataByPath to useForm table (#12098)

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Fixes #

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### What?
This PR adds the `getDataByPath` utility function to the `useForm` table
in the docs.

### Why?
This utility is useful for dealing with arrays and other form state.
Users commonly ask for examples on how to deal with arrays when using
`useField` as this function will return a length instead of the expected
value object.

### How?
Addition of `getDataByPath` to the `useForm` object table in
`docs/admin/react-hooks.mdx`.

Author: akhrarovsaid

docs/admin/react-hooks.mdx

@@ -348,6 +348,17 @@ The `useForm` hook returns an object with the following properties:
         value: '',
       },
     ],
+    [
+      {
+        value: "**`getDataByPath`**",
+      },
+      {
+        value: 'Returns form field data for the given field path. Useful when dealing with arrays, blocks, or other form state.',
+      },
+      {
+        value: '',
+      },
+    ],
     [
       {
         value: "**`setModified`**",