Disable horizontal merge between header and body cells.

[aStewartDesign]

Fix: Disable horizontal cell merges between header and body cells. Closes ckeditor/ckeditor5#5744.

NOTE: Prevents merging between column header cells and body cells

Additional information

This assumes this is the direction to take on the issue documented here: ckeditor/ckeditor5#5744

[aStewartDesign]

Where do I submit the CLA? If here works then here it is:
Signed CLA

[coveralls]

Coverage remained the same at 100.0% when pulling fcba087 on aStewartDesign:t/ckeditor5/5744 into 63da06f on ckeditor:master.

[jodator]

Hello again, @aStewartDesign!

Thanks for the PR :)

The only thing that was missing is handling the cases when cells are spanned. Spanned cells always add complexity to the general solution.

I'll link to the commit with the changes for reference when I marge the PR.

[jodator]

@aStewartDesign did you sign the CLA? I've missed this and probably we need this to merge your PR. If you have any problems (probably no email in GH) you can write to us on https://ckeditor.com/contact/ with a link to this PR and we will send you the CLA request manually.

Thanks!

[vokiel]

@aStewartDesign we noticed that you've attached the manually signed CLA where we can find your current email (different from the one we got from GH).

If it's not a problem for you, could you please sign the electronic CLA so we will have all in order and confirmed by our electronic signature provider? You should receive link on your email. Thanks!

[aStewartDesign]

@vokiel not a problem! All signed and should be good to go. Thank you!

[jodator]

@aStewartDesign thanks for the input!

The changes that I've mentioned are here: c98cfa6.

[Reinmar]

It turned out that this change caused a quite serious regression: ckeditor/ckeditor5#6368.