Merging branch 'j.1'  into 'main'.

See merge request !2284

Merging branch 'j.1'  into 'main'.

See merge request !2283

Merging branch 'a.addPyCoreTests'  into 'main'.
related to issue #223

See merge request !2274

To avoid a clash with the system's default Python, a virtual enviroment (Python venv)
is created and employed.

Such a function is needed to get version strings.

Merging branch 'j.883sf1'  into 'main'.

See merge request !2282

Merging branch 'j.restart'  into 'main'.

See merge request !2281

MaskEditorCanvas::updateMaskCanvas repaint only after setting data => mask canvas now shown from the beginning in full size