docs: release notes for the v21.0.0-rc.4 release #9965

Job	Run time
lint	2m 24s
build	2m 9s
analyze	7s
build-e2e-windows-subset	2m 26s
test	3m 50s
e2e-package-managers (ubuntu-latest-4core, 22, yarn, 0)	8m 28s
e2e-package-managers (ubuntu-latest-4core, 22, pnpm, 0)	6m 19s
e2e-package-managers (ubuntu-latest-4core, 22, pnpm, 2)	6m 28s
e2e-package-managers (ubuntu-latest-4core, 22, yarn, 2)	7m 29s
e2e-package-managers (ubuntu-latest-4core, 22, yarn, 1)	6m 22s
e2e-package-managers (ubuntu-latest-4core, 22, pnpm, 1)	4m 49s
e2e (ubuntu-latest, 22, npm, 0)	10m 58s
e2e (ubuntu-latest, 22, esbuild, 0)	7m 45s
e2e (ubuntu-latest, 22, npm, 2)	10m 21s
e2e (ubuntu-latest, 22, npm, 1)	11m 48s
e2e (ubuntu-latest, 22, npm, 4)	9m 18s
e2e (ubuntu-latest, 22, npm, 3)	8m 38s
e2e (ubuntu-latest, 22, esbuild, 3)	8m 13s
e2e (ubuntu-latest, 22, esbuild, 4)	6m 33s
e2e (ubuntu-latest, 22, esbuild, 1)	9m 21s
e2e (ubuntu-latest, 22, esbuild, 2)	9m 36s
e2e (ubuntu-latest, 22, esbuild, 5)	9m 42s
e2e (ubuntu-latest, 22, npm, 5)	10m 6s
e2e-snapshots	0s
e2e-windows-subset	4m 31s
	2h 47m 41s

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