[Mac] Brush editor not keyboard navigable

[ermau]

Tabbing through properties skips right over brush editors in name arranged mode.

VS bug #703875

[bleroy]

This actually works once you enable tab stops on all controls in macos settings (keyboard / shortcuts). It doesn't stop on Booleans / flags or brushes unless you set this up. Once you do though, predefined values (that are not flags, so shown in a drop down) do not get tab stops.

The tab order between the header and the property table in the standalone is also all wrong.

[bleroy]

Pull request #467 makes it possible to open the popup by hitting space or enter when the brush property is in focus. Keyboard navigation inside the popup still needs to be fixed.