Previously the method in QgsGeometryUtils was relying on
QgsAbstractGeometry::coordinateSequence, which is an absolute
performance killer.
Instead move to optimised methods in the various abstract
geometry subclasses which rely only on trivial calculations.
Adds a new geometry class for Triangle geometries
Methods include orthocenter, bisectors, medians, medial, circumscribed (center,
radius), inscribed (center, radius)
Also adds make_triangle expression function for creating triangles
