Optimise the logic used when the new geometry backend for
selective masking is in effect:
Whenever its SAFE, instead of calculating an "entire map" clipping
path and then applying this for every feature being rendered,
we now defer the calculation of the clipping path until we
are rendering individual features. Then, we create a clipping path
which contains ONLY the mask paths which are within the area
being drawn over.
This avoids having the entire map clipping path being used for
EVERY feature being rendered, which results in huge PDF/SVG
exports when masks are in effect, and instead results in
clipping paths which are confined just to a sensible area
around each rendered feature.
In some complex test projects this reduces the PDF export
size by a factor of 0.01!! (and results in PDFs/SVGs which
open much quicker in viewers and editors, and don't grind
their operation to a halt).
0ca28af9a0