tree-sitter: further improve parsing of nested comments, extend tests #175

Job	Run time
build (ubuntu-20.04, debug)	28s
build (ubuntu-20.04, dev)	36s
build (ubuntu-20.04, release)	1m 19s
build (macos-latest, debug)	1m 25s
build (macos-latest, dev)	1m 47s
build (macos-latest, release)	3m 7s
build (windows-latest, debug)	1m 55s
build (windows-latest, dev)	1m 49s
build (windows-latest, release)	2m 54s
	15m 20s

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