Allow FloatingToolbar to be outside of the attached window.

Currently PopupWindow used for the floating toolbar specifies
neither FLAG_LAYOUT_NO_LIMITS nor FLAG_LAYOUT_IN_SCREEN.
As a result, the floating toolbar can overlap the selected
text when the attached window does not have enough height.

Here is the repro code.

    final TextView textView = new TextView(this);
    textView.setLayoutParams(
            new ViewGroup.LayoutParams(
                    ViewGroup.LayoutParams.MATCH_PARENT,
                    ViewGroup.LayoutParams.WRAP_CONTENT));
    textView.setText("A test sentence.");
    textView.setTextIsSelectable(true);
    final AlertDialog dialog = new AlertDialog.Builder(this)
            .setView(textView)
            .create();
    dialog.getWindow().setGravity(Gravity.BOTTOM)
    dialog.show();

If you tap a word in the dialog, the floating toolbar
unintentionally overlaps the selected text due to the limited
height of the AlertDialog.

It also turns out that just calling
  PopupWindow.setClippingEnabled(false)
to specify FLAG_LAYOUT_NO_LIMITS is not sufficient and ends up
showing the toolbar on the NavBar because we have mistakenly
compared bounds in window-local coordinates
(e.g. FloatingActionModemContentRectOnWindow) with bounds in
screen coordinates (e.g. FloatingActionMode#mScreenRect).
Hence the confusion of window-local coordinates and screen
coordinates in FloatingToolbar and FloatingToolbar also needs
to be addresses.

To summarize here are the notable changes in this CL:
  - Specify FLAG_LAYOUT_NO_LIMITS so that the floating
    toolbar can be placed outside of the attached window.
    (We do this with PopupWindow#setClippingEnabled)
  - Switch to use screen coordinates from window-local
    coordiantes in FloatingToolbar and FloatingActionMode
    because some system components such as WindowManager
    prefer screen coordinates.
  - Put -OnScreen suffix for Rect and Point variables
    as long as they are in screen coordinates.

Bug: 22335001
Change-Id: I71a8d356e868dc7715b030ca1078da4ec39368c3