refactor(FormHelper): update to use InertiaFormRunes type

Replace InertiaForm with InertiaFormRunes in Generic.svelte to align with updated type definitions from @inertiajs/svelte5. Adjust form prop usage to destructure from $props().

Author: brodienguyen

packages/svelte5/test-app/Pages/FormHelper/TypeScript/Generic.svelte

@@ -1,9 +1,9 @@
 <script lang="ts" generics="TFormData extends Record<string, FormDataConvertible>">
   // This component is used for checking the TypeScript implementation; there is no Playwright test depending on it.
   import type { FormDataConvertible } from '@inertiajs/core'
-  import type { InertiaForm } from '@inertiajs/svelte5'
+  import type { InertiaFormRunes } from '@inertiajs/svelte5'
 
-  export let form: InertiaForm<TFormData>
+  const { form }: { form: InertiaFormRunes<TFormData> } = $props()
 </script>
 
 <div>{form}</div>