Add option to treat some chars also as "auto bracket" only when we have a selection

With that option you can add e.g. Markdown markups, or what ever else may handy,
afterwards to some text like you can do with quotes and enabled auto brackets.

The combobox option for that feature offer a few suggestions which you can
modify as you like which will add a new char set. Clear the set, e.g. by the
line edit button, will remove the set from the combobox. The default suggestions
can't be removed.

Differential Revision: https://phabricator.kde.org/D17693