revert to pre react 16 popover and calc popover height before tether positions things(#15608)

* revert popover to before react 16 changes

* move tether/sizeToFit logic to render callback

* set ParameterFieldWidget free

* add debounce to maxheight futzing

* do popover height calc BEFORE updating tether when attached above target

* do height calcs for both top/bottom before tether stuff

* ignore tetherOptions prop