Add simple terrain implementation #259

Job	Run time
build (stable, ubuntu-latest)	2m 37s
build (nightly, ubuntu-latest)	2m 40s
build (stable, windows-latest)	4m 12s
build (nightly, macos-latest)	2m 28s
build (nightly, windows-latest)	4m 23s
build (stable, macos-latest)	2m 48s
	19m 8s

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