Decouple horiz scrolling in inline text editors from outer editor.
As part of this, make the related container a simple child of the widget, so
we no longer have to do all the various hacks to position it.
Merge from cmv3
Merge pull request #2500 from adobe/nj/cmv3-inline-hscroll

[cmv3] Decouple horiz scrolling in inline text editors from outer editor.