fixed closestSegmentWithContext() params in Python

[blazek]

Missing QgsGeometry.closestSegmentWithContext() in Python bindings.

[nyalldawson]

@blazek I've noticed something very inconsistent here - QgsGeometry::closestSegmentWithContext < 0 for points to the right and > 0 for points to the left, yet QgsGeometryUtils::leftOfLine uses < 0 for left and > 0 for right.

Additionally, QgsAbstractGeometry::closestSegment uses a bool for leftOf - which means that the case when leftOf is 0 from QgsGeometryUtils::leftOfLine is treated as "point to the right", instead of the correct "unknown" intrepretation (e.g. point exactly on a line). I think we need to fix all these methods to use an int for leftOf, with a consistent < / > 0 behaviour.

[nyalldawson]

Superseded by #5758

[blazek]

I have just fixed the documentation of QgsGeometry::closestSegmentWithContext to what it really returns. Originally it was also < 0 for left and > 0 for right.