feat: add extendEmptyMarkRange option to mark commands

[philippkuehn]

This PR adds an option extendEmptyMarkRange to the unsetMark and toggleMark commands. This defaults to false now (until now it was true). This option is useful for the link mark, to remove a link even if there is an empty selection but it’s rather confusing for other marks.

Thanks for @isubasti for the main idea (#1650).

[isubasti]

Hi @philippkuehn thanks for this. Though there is one more corner case on this one but haven't got a chance to think about it. it's for things like two link marks that are next to each other with different attrs then if the empty selection is on the first one then only the first one should be removed instead of removing mark for both.

[philippkuehn]

ah you are right! will look at this later! (we just need to pass the current mark attributes to getMarkRange)

[philippkuehn]

should be fixed with this patch.