Inverted renderer: make sure it works when no painter is here (feature count)
Inverted polygon renderer: add an option to preprocess polygons using an union
Inverted polygon renderer: make sure the each symbol category is always rendered in the same order
Inverted polygon renderer: fix rendering when projection is enabled
Inverted polygon renderer: add test for projected and merged
Inverted polygon renderer: update SIP
Fixed indentation
Fix #10355 (crash) and #10338 (overlapping polygons) in inverted polygon renderer

Conflicts:
	python/core/symbology-ng/qgsinvertedpolygonrenderer.sip
	src/core/symbology-ng/qgsinvertedpolygonrenderer.cpp
	src/core/symbology-ng/qgsinvertedpolygonrenderer.h
	src/gui/symbology-ng/qgsinvertedpolygonrendererwidget.cpp
	src/gui/symbology-ng/qgsinvertedpolygonrendererwidget.h
Allow some mismatched pixels in inverted renderer test

On my machine, there were ~200-800 mismatched pixels in each test image,
but visually they look the same.
Small renaming of typedef / member variable
Build "multi" only when it's needed