Add a modifier to make particles round. #556

Job	Run time
run-examples	11m 50s
Check format	1m 3s
build (2d, stable, windows-latest)	8m 27s
Coverage	5m 17s
build (2d, stable, ubuntu-latest)	12m 43s
build (2d, stable, macos-latest)	2m 21s
build (3d, stable, windows-latest)	7m 48s
build (3d, stable, ubuntu-latest)	11m 37s
build (3d, stable, macos-latest)	1m 58s
build (all, stable, windows-latest)	6m 57s
build (all, stable, ubuntu-latest)	8m 17s
build (all, stable, macos-latest)	6m 4s
	1h 24m 22s

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