Don't emit Surface changes back to the Surface

modules/ve/ce/ve.ce.SurfaceObserver.js
* add emitContentChanges argument to poll (and start and stop)

modules/ve/ce/ve.ce.Surface.js
* Pass emitContentChanges=false to calls to start/stop in certain places
* Explicitly pass emitContentChanges=true elsewhere, to preserve prior
  behaviour

modules/ve/ui/ve.ui.Surface.js
* Explicitly pass emitContentChanges=true to poll

modules/ve/test/ve.test.js
* Escape non-BMP unicode text literals (to prevent potential editor
  problems)

Bug: 50105
Bug: 50346
Bug: 50631
Bug: 51477
Bug: 52716
Change-Id: I19ec7eaa0e3224cbfc7e7188e964183d7393c9a7
Merge "Don't emit Surface changes back to the Surface"