Add `@Snapshot` as built-in extension (#1873) #386

Job	Run time
build-and-verify (ubuntu-latest, 2.5, 8)	6m 24s
build-and-verify (ubuntu-latest, 2.5, 11)	4m 46s
build-and-verify (ubuntu-latest, 3.0, 8)	6m 43s
build-and-verify (ubuntu-latest, 3.0, 11)	5m 5s
build-and-verify (ubuntu-latest, 3.0, 17)	5m 18s
build-and-verify (ubuntu-latest, 3.0, 21)	5m 16s
build-and-verify (ubuntu-latest, 4.0, 8)	8m 24s
build-and-verify (ubuntu-latest, 4.0, 11)	6m 33s
build-and-verify (ubuntu-latest, 4.0, 17)	5m 16s
build-and-verify (ubuntu-latest, 4.0, 21)	4m 33s
build-and-verify (windows-latest, 2.5, 8)	6m 5s
build-and-verify (windows-latest, 3.0, 8)	7m 7s
build-and-verify (windows-latest, 4.0, 8)	6m 42s
build-and-verify (macos-latest, 2.5, 8)	7m 34s
build-and-verify (macos-latest, 3.0, 8)	8m 5s
build-and-verify (macos-latest, 4.0, 8)	6m 58s
release-spock	0s
publish-release-docs	0s
	1h 40m 49s

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