Summary:
This commit introduces the behaviour of Clone Brush
that allows for always starting a new stroke
as if the offset wasn't set yet, which means it always
starts from the same source/origin point.
Usecases: painting multiple leaves, flowers, crosses etc.
in less regular way than what could be created with regular
Clone Brush.

BUG:402559

Test Plan:
- save and load brush with and without the new option enabled
- use the same brush with and without the new option enabled
- use both versions without setting the origin
- switch between enabled and disabled option after setting the origin
- check whether the tooltip works

Reviewers: #krita, dkazakov

Reviewed By: #krita, dkazakov

Subscribers: dkazakov

Tags: #krita

Differential Revision: https://phabricator.kde.org/D20653