fix(react18): forwardRef Popover wrapper, wrap explore popover trigger children in span

- Popover (superset-ui-core): forward refs to antd Popover so consumers that
  pass it as a trigger child can attach a DOM ref without triggering findDOMNode.
- Explore popover triggers (ColorBreakpoint, Contour, DndColumnSelect, AdhocFilter):
  the popover children are arbitrary user nodes which are often function
  components without forwardRef. Wrapping them in a span gives antd's resize
  observer a real DOM ref to attach, eliminating the React 18 deprecation warning.

superset-frontend/packages/superset-ui-core/src/components/Popover/index.tsx

@@ -16,11 +16,14 @@
  * specific language governing permissions and limitations
  * under the License.
  */
-import { Popover as AntdPopover } from 'antd';
+import { forwardRef } from 'react';
+import { Popover as AntdPopover, type TooltipRef } from 'antd';
 import { PopoverProps as AntdPopoverProps } from 'antd/es/popover';
 
 export interface PopoverProps extends AntdPopoverProps {
   forceRender?: boolean;
 }
 
-export const Popover = (props: PopoverProps) => <AntdPopover {...props} />;
+export const Popover = forwardRef<TooltipRef, PopoverProps>((props, ref) => (
+  <AntdPopover ref={ref} {...props} />
+));

superset-frontend/src/explore/components/controls/ColorBreakpointsControl/ColorBreakpointPopoverTrigger.tsx

@@ -54,7 +54,9 @@ const ColorBreakpointsPopoverTrigger = ({
       onOpenChange={setVisibility}
       destroyOnHidden
     >
-      {props.children}
+      {/* Wrap in span so the Popover can attach a ref without relying
+          on findDOMNode (deprecated in React 18+). */}
+      <span>{props.children}</span>
     </ControlPopover>
   );
 };

superset-frontend/src/explore/components/controls/ContourControl/ContourPopoverTrigger.tsx

@@ -52,7 +52,9 @@ const ContourPopoverTrigger = ({
       onOpenChange={setVisibility}
       destroyOnHidden
     >
-      {props.children}
+      {/* Wrap in span so the Popover can attach a ref without relying
+          on findDOMNode (deprecated in React 18+). */}
+      <span>{props.children}</span>
     </ControlPopover>
   );
 };

superset-frontend/src/explore/components/controls/DndColumnSelectControl/ColumnSelectPopoverTrigger.tsx

@@ -201,7 +201,9 @@ const ColumnSelectPopoverTriggerInner = ({
         title={popoverTitle}
         destroyOnHidden
       >
-        {children}
+        {/* Wrap in span so the Popover can attach a ref without relying
+            on findDOMNode (deprecated in React 18+). */}
+        <span>{children}</span>
       </ControlPopover>
     </>
   );

superset-frontend/src/explore/components/controls/FilterControl/AdhocFilterPopoverTrigger/index.tsx

@@ -112,7 +112,9 @@ class AdhocFilterPopoverTrigger extends PureComponent<
         onOpenChange={togglePopover}
         destroyOnHidden
       >
-        {this.props.children}
+        {/* Wrap in span so the Popover can attach a ref without relying
+            on findDOMNode (deprecated in React 18+). */}
+        <span>{this.props.children}</span>
       </ControlPopover>
     );
   }