Instead of requiring all linestrings to be constructed by
first creating QgsPointSequence (requiring creation or
conversion of points to QgsPointV2), allow construction
of LineStrings directly from vectors of values (fastest!)
or lists of QgsPoint.
Likely results in speedups for lots of geometry operations,
but using the same layer as earlier tested for densify
improvements the densify operation time dropped further
from 25 seconds to 15 seconds.
Faster than QgsGeometry::isGeosEmpty() because it avoids the
conversion to GEOS geometries and just uses the QgsAbstractGeometry
subclasses directly.
Also implements faster isEmpty() overrides for specific
QgsAbstractGeometry subclasses.
Make nCoordinates virtual, and provide shortcuts for some
geometry types. The base method which calls coordinateSequence()
is quite slow in certain circumstances.
Speeds up rendering point layers by ~25%, also likely to
speed up lots of geometry heavy operations throughout QGIS
Refs #15752
