I/6119: Clear table contents on clipboard "cut" and keyboard delete

[jodator]

Suggested merge commit message (convention)

Feature: Clear table contents on clipboard "cut" and keyboard delete. Closes ckeditor/ckeditor5#6119. Closes ckeditor/ckeditor5#6284. Closes ckeditor/ckeditor5#6301.

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Additional information

For the "cut" event handler I had to override (thus duplicate) default Clipboard plugin behavior which was removing a single range instead of multi-range selection. This could be simplified by enhancing model.deleteContent() (reported here: ckeditor/ckeditor5#6328).

[coveralls]

Coverage remained the same at 100.0% when pulling f3c356d on i/6119 into 50fe737 on master.

[Reinmar]

For the "cut" event handler I had to override (thus duplicate) default Clipboard plugin behavior which was removing a single range instead of multi-range selection. This could be simplified by enhancing model.deleteContent() (reported here: ckeditor/ckeditor5#6328).

I think that improving deleteContent() and insertContent() is a must. Most features use those methods so we'll need to do that for ckeditor/ckeditor5#6301, ckeditor/ckeditor5#6284 and ckeditor/ckeditor5#6116. But we can live with that for a second.

[jodator]

@Reinmar So I've checked the state of the deleteContent(). ATM (this PR) we have a safe thing that works. Upgrading the model.deleteContent() with directionality (ckeditor/ckeditor5#3115) could be done in a separate ticket.

From what I can see this PR fixes also (see closes in the first post):

• enter
• typing

over selected table fragment.

it does not, however, fix the ckeditor/ckeditor5#6346 - which is required for UNDO to work :/ Ps.: IMO separate PR/ticket.