[tree_sitter_v] Support `for mut is` clause #180

Job	Run time
build (ubuntu-20.04, debug)	27s
build (ubuntu-20.04, dev)	33s
build (ubuntu-20.04, release)	1m 17s
build (macos-latest, debug)	1m 44s
build (macos-latest, dev)	1m 9s
build (macos-latest, release)	2m 3s
build (windows-latest, debug)	1m 45s
build (windows-latest, dev)	2m 8s
build (windows-latest, release)	2m 59s
	14m 5s

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