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.