all: support extra commands, `vab <cmd>` where `<cmd>` comes from `va… #582

Job	Run time
build-legacy-v-examples-as-apk-and-aab (ubuntu-20.04, 8, 31)	6m 26s
build-legacy-v-examples-as-apk-and-aab (ubuntu-20.04, 8, 33)	7m 7s
build-v-examples-as-apk-and-aab (ubuntu-20.04, 11, 31)	5m 24s
build-v-examples-as-apk-and-aab (ubuntu-20.04, 11, 33)	5m 23s
build-v-examples-with-gc-disabled (ubuntu-20.04, 11, 31)	4m 21s
build-v-examples-as-apk-and-aab (ubuntu-20.04, 15, 31)	5m 24s
build-v-examples-with-gc-disabled (ubuntu-20.04, 11, 33)	3m 57s
build-v-examples-as-apk-and-aab (ubuntu-20.04, 15, 33)	5m 11s
build-v-examples-with-gc-disabled (ubuntu-20.04, 15, 31)	3m 48s
build-v-examples-as-apk-and-aab (ubuntu-20.04, 20, 31)	5m 3s
build-v-examples-with-gc-disabled (ubuntu-20.04, 15, 33)	4m 20s
build-v-examples-as-apk-and-aab (ubuntu-20.04, 20, 33)	5m 25s
build-v-examples-with-gc-disabled (ubuntu-20.04, 20, 31)	4m 12s
build-v-examples-with-gc-disabled (ubuntu-20.04, 20, 33)	4m 52s
	1h 10m 53s

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