[Definition Section] Add automatic resize for pinned definition section with double click on the boarder

[rherrmannr]

Functionality, which is used in the old definition section. Width of Definition Section depending on the max length of the declarations/comments

[andreasmuelder]

I think the old definition section is replaced with the new pinned editor so we should not add features to the old one...

[andreasmuelder]

reopen, this feature is related to the new pinned editor.