fix(react-form): default selector to identity in Subscribe component

When <form.Subscribe> is rendered without a selector prop, it crashes
at runtime because useStore receives undefined as the selector:

  TypeError: selector is not a function

The types already mark selector as optional, so the runtime behavior
should match. This adds a default identity function ((state) => state)
for the selector parameter in both LocalSubscribe implementations
(useForm and useFieldGroup).

Fixes #2063

Author: isaackaara

packages/react-form/src/useFieldGroup.tsx

@@ -23,11 +23,11 @@ import type { LensFieldComponent } from './useField'
 
 function LocalSubscribe({
   lens,
-  selector,
+  selector = (state) => state,
   children,
 }: PropsWithChildren<{
   lens: AnyFieldGroupApi
-  selector: (state: FieldGroupState<any>) => FieldGroupState<any>
+  selector?: (state: FieldGroupState<any>) => FieldGroupState<any>
 }>): ReturnType<FunctionComponent> {
   const data = useStore(lens.store, selector)
 

packages/react-form/src/useForm.tsx

@@ -139,11 +139,11 @@ export type ReactFormExtendedApi<
 
 function LocalSubscribe({
   form,
-  selector,
+  selector = (state) => state,
   children,
 }: PropsWithChildren<{
   form: AnyFormApi
-  selector: (state: AnyFormState) => AnyFormState
+  selector?: (state: AnyFormState) => AnyFormState
 }>): ReturnType<FunctionComponent> {
   const data = useStore(form.store, selector)