Widgets: Error thrown when moving focus from widget to editable by elements path

[Marek Lewandowski]

After talk with PK we decided to create yet separate ticket for original issue reported in #10869, since issue required more sophisticated solution.

1. Open samples/plugins/image2/image2.html
2. Select a widget.
3. In elementspath, click "body"
4. An error is thrown (Chrome, Firefox):

   Uncaught IndexSizeError: Index or size was negative, or greater than the allowed value. 
   

   IE9:

   SCRIPT5022: DOM Exception: INDEX_SIZE_ERR (1) 
   

additional info:

1. Issue is caused because hiddenSelectionContainer is not removed in right time, and created selection has offset bigger by one.
2. editor.getSelection().reset() call placed before range.selectNodeContents( element ) statement did the job, however it should be placed somewhere deeper to be reused. Maybe selectNodeContents itself?
3. this issue is originated from #10869

[Piotrek Koszuliński]

Rearranged tickets due to new ones which have high priority.

[Olek Nowodziński]

Pushed solution to ​t/11021 (+corresponding test branch).

[Piotrek Koszuliński]

I pushed additional commits to dev and tests to fix following issues:

• tests were not passing in some IEs because too precise ranges comparison didn't assume selection engines differences,
• patch for dev was breaking all selections anchored in editable, because it didn't check if hidden selection container exists; TC: place caret anywhere, press body in elements path,
• patch for dev did not fix ranges for MS selections.

[Olek Nowodziński]

​git:ebd3500 landed in master (fe71804 tests).