Make Flex take ReactNode children (#2260)

Co-authored-by: Danni <[email protected]>

Author: solimant

packages/@react-types/layout/src/flex.d.ts

@@ -11,11 +11,11 @@
  */
 
 import {DOMProps, FlexStyleProps} from '@react-types/shared';
-import {ReactElement} from 'react';
+import {ReactNode} from 'react';
 
 export type Slots = {[key: string]: any};
 
 export interface FlexProps extends DOMProps, FlexStyleProps {
   /** Children of the flex container. */
-  children: ReactElement | ReactElement[]
+  children: ReactNode
 }