Fix: Error thrown when navigating into the table insertion panel using the keyboard.

[jodator]

Suggested merge commit message (convention)

Fix: Error thrown when navigating into the table insertion panel using the keyboard. Closes ckeditor/ckeditor5#3182.

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Additional information

• I've simply removed the error by adding missing dummy methods. The core issue is that this view does not have keyboard support (Add keyboard support for insert table dropdown ckeditor5#3176). So I'd fix the error here and implement Add keyboard support for insert table dropdown ckeditor5#3176 with proper keyboard support either before or after the initial release.

[coveralls]

Coverage remained the same at 100.0% when pulling d05db3c on t/40 into db1cd82 on master.