Fix sizing and scrolling issues from latest upstream-master

@njx Fixes #2655, #2523, #2521.

* Handle ``redraw`` event on the widget (from the host editor) and refresh inline instances of CodeMirror
* Consolidate ``sizeInlineWidgetToContents()`` calls into an ``update`` event listener. Whenever an inline editor update's it's display, we force a new height on the inline widget container

I'm also seeing #2657 fixed in my branch. But I'm not sure how my changes would have affected horizontal scrolling.