Widgets: Keyboard events prevention while focused

[Marek Lewandowski]

Widgets: Keyboard events prevention while focused

since: 4.3beta (didn't check earlier) until major

Occurs in all browsers.

1. open any image2 pluigin sample (i.e. plugins/image2/samples/image2.html)
2. click on image (in order to focus it, blue outline should appear)
3. press alt+f10

Expected result:
Toolbar should be focused.

Current result:
Focus stays at image widget.

Additional info:

1. issue does not occurs within content editable.
2. it also prevents lots of browser hotkeys, like chromium alt+d (address bar highlight).
3. here's line which may be modified in order to solve the problem: ​https://github.com/ckeditor/ckeditor-dev/blob/major/plugins/widget/plugin.js#L2332

simple idea would be to add || ( CKEDITOR.ALT & keyCode ) But there still end user may experience some issue, with other browser hotkeys, i.e. in chromium based browsers pressing (just) F6 will cycle focus between browsers top ui elements, like address bar, bookmarks, extensions icons

Suggestion:
We may also add handling for tab key, for jumping to next element