prefer deprecated prop over context to make this a non-breaking change

Author: LFDanLu

packages/@react-aria/overlays/src/Overlay.tsx

@@ -57,7 +57,7 @@ export function Overlay(props: OverlayProps): ReactNode | null {
   let contextValue = useMemo(() => ({contain, setContain}), [contain, setContain]);
 
   let {getContainer} = useUNSTABLE_PortalContext();
-  if (getContainer) {
+  if (!props.portalContainer && getContainer) {
     portalContainer = getContainer();
   }
 

packages/@react-aria/overlays/src/useModal.tsx

@@ -129,7 +129,7 @@ export function OverlayContainer(props: OverlayContainerProps): React.ReactPorta
   let isSSR = useIsSSR();
   let {portalContainer = isSSR ? null : document.body, ...rest} = props;
   let {getContainer} = useUNSTABLE_PortalContext();
-  if (getContainer) {
+  if (!props.portalContainer && getContainer) {
     portalContainer = getContainer();
   }