Block widget DnD should behave similar to other DnD

[Piotr Jasiun]

1. Block widgets DnD should fire paste events.
2. Block widgets DnD should fire editor.dragstart, editor.dragend and editor.drop events.
3. Paste event should have additional parameter range so it should be possible to paste between blocks, where we can not set selection.
4. Some widget DnD clean-up is needed to remove leftovers.

This ticket should fix: #11219 and #12090.

[Piotr Jasiun]

Changes are done and pushed to the ​t/13042 branch. The most important changes are listed below.

• Drag and Drop dataTransfer is now always bind for all events since last reset, if there is no native event.
• Clipboard D&D logic is now moved to the editor.drag|dropstart|dropend events listeners. This means that it is enough to fire these events with proper parameters (target and ranges) to execute drag and drop.
• Block widgets use editor.drag|dropstart|dropend events.
• Block and inline widgets now share part of the D&D code.
• extractHtmlFromRange has now removeEmptyBlock parameter.
• editor.insertHtml and editable.insertHtml have now the range parameter.
• widgets use now extractHtmlFromRange instead of outerHtml.

This ticket needed 2 other to be closed: #13069, #13101.

After these changes 2 bugs were introduced, they will be reported as separate tickets:

• block widget is not focused after undo (#13129),
• ids are removed (#13128).

These changes should fix: #11219, #12090, #12095.

[Piotrek Koszuliński]

Closed with ​git:1b974b7. Hurray!