Simple fix to make scrolling in Quick Docs less painful: when cursor is
over Quick Docs details area, never let scrollwheel/trackpad scroll the
host editor. (If the docs scroller is already maxed out, do nothing at all).
Fix issues with Quick Docs viewer's scroll trapping:
* Need to stopPropagation() or host CodeMirror editor may programmatically
scroll in some cases. (In testing, seems to only happen when making a diagonal
trackpad motion on Mac -- i.e. when wheelDeltaX/Y are both nonzero).
* Don't block scroll events when docs content doesn't need scrollbars - let
host editor scroll naturally in that case.
Merge pull request #3499 from adobe/pflynn/trap-mousewheel

Make mousewheel/trackpad scrolling in Quick Docs less painful