Deprecate `OverlayPortal.targetsRootOverlay`

The OverlayPortal.targetsRootOverlay property was deprecated and replaced with overlayLocation.

A parameter overlayLocation was added to the OverlayPortal default constructor to control where the overlay child renders. As the result, the constructor OverlayPortal.targetsRootOverlay was no longer useful.

The OverlayPortal.targetsRootOverlay was deprecated.

If you are using OverlayPortal.targetsRootOverlay, you can use OverlayPortal with overlayLocation instead.

Code before migration:

dartWidget build(BuildContext context) {
  return OverlayPortal.targetsRootOverlay(
    controller: myController,
    overlayChildBuilder: _myBuilder,
    child: myChild,
  );
}

Code after migration:

dartWidget build(BuildContext context) {
  return OverlayPortal(
    overlayLocation: OverlayChildLocation.rootOverlay,
    controller: myController,
    overlayChildBuilder: _myBuilder,
    child: myChild,
  );
}