This refactor includes:
- In Lua now we can clone a custom brush with Brush(Image) and the new
brush doesn't share the image with the original one (added a new test
for this).
- Avoid creating extra images when it's not needed using
Brush::cloneWithExistingImages() (we can inject existing images in
the brush itself).
- Delete Brush-copy contructor & assign operator to use
Brush::clone() functions instead (which are more explicit).
- Some code from 12d81352647e96c8ac6d70e4a252c37ce5a29ade (#4023)
reverted to avoid recreating brushes on left-click or in the brush
preview, i.e. moving the mouse (#4013 refers only to right-click, so
only on right-click we have to adjust the custom brush).
92edd5f700