Implements a method in QgsGeometry and a processing algorithm to
calculate the pole of inaccessibility for a surface, which is the
most distant internal point from the boundary of the surface. This function
uses the 'polylabel' algorithm (Vladimir Agafonkin, 2016), which is an iterative
approach guaranteed to find the true pole of inaccessibility within a specified
tolerance. More precise tolerances require more iterations and will take longer
to calculate.
