feat(useForm): add reactive getters for form data

Introduce reactive getters for all form data properties in the useForm hook. This allows consumers to access form fields reactively, improving reactivity and consistency in Svelte components.

Author: brodienguyen

packages/svelte5/src/useForm.svelte.ts

@@ -103,8 +103,16 @@ export default function useForm<TForm extends FormDataType<TForm>>(
     }
   }
 
+  // Create reactive getters for all form data properties
+  const formDataGetters = Object.keys(initialData).reduce((carry, key) => {
+    return {
+      ...carry,
+      get [key]() { return get(formData, key) }
+    }
+  }, {} as TForm)
+
   const form: InertiaFormRunes<TForm> = {
-    ...formData,
+    ...formDataGetters,
     get isDirty() { return isDirty },
     get errors() { return errors },
     get hasErrors() { return hasErrors },