[@mantine/form] Fix nodenext resolutions (#8260)

Author: rtivital

packages/@mantine/form/src/index.ts

@@ -1,11 +1,11 @@
-export { useForm } from './use-form';
-export { createFormContext } from './FormProvider/FormProvider';
+export { useForm } from './use-form.js';
+export { createFormContext } from './FormProvider/FormProvider.js';
 export { createFormActions } from './actions/index.js';
-export { Form } from './Form/Form';
-export { FORM_INDEX } from './form-index';
+export { Form } from './Form/Form.js';
+export { FORM_INDEX } from './form-index.js';
 export * from './validators/index.js';
-export { useField } from './use-field';
-export { formRootRule } from './validate/validate-values';
+export { useField } from './use-field.js';
+export { formRootRule } from './validate/validate-values.js';
 
 export { zodResolver } from './resolvers/zod-resolver/zod-resolver';
 export { superstructResolver } from './resolvers/superstruct-resolver/superstruct-resolver';