Implemented anisotropic spacing for the Krita brushes

Now if you change the 'ratio' option the brush, the horizontal
and vertical spacing will be relative to the width and height of the
brush correspondingly.

This effect is achieved by used equation of a ellipse. When the
cumulative 'distance' value grows out of the ellipse defined by the
spacing values, a new dab is painted.

BUG:276465