tree-sitter: further improve parsing of nested comments, extend tests #176

Job	Run time
build (ubuntu-20.04, debug)	27s
build (ubuntu-20.04, dev)	26s
build (ubuntu-20.04, release)	1m 20s
build (macos-latest, debug)	1m 15s
build (macos-latest, dev)	1m 15s
build (macos-latest, release)	2m 24s
build (windows-latest, debug)	1m 47s
build (windows-latest, dev)	1m 51s
build (windows-latest, release)	3m 9s
	13m 54s

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