release: cut the v21.0.0-rc.0 release #2244

Job	Run time
build-e2e-windows	31s
build	29s
lint	2m 16s
publish-snapshots	0s
Browser Compatibility Tests	0s
e2e	0s
test	0s
e2e-snapshots	0s
e2e-package-managers	0s
e2e-windows	0s
	3m 16s

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