docs: release notes for the v21.0.0-rc.2 release #9176

Job	Run time
lint	2m 10s
build	2m 18s
build-e2e-windows	2m 45s
test	1m 45s
Browser Compatibility Tests	1m 43s
publish-snapshots	1m 33s
e2e-windows (windows-2025, 22, npm, 0)	1m 7s
e2e-windows (windows-2025, 22, npm, 4)	1m 12s
e2e-windows (windows-2025, 22, npm, 2)	1m 16s
e2e-windows (windows-2025, 22, npm, 3)	1m 5s
e2e-windows (windows-2025, 22, npm, 1)	1m 17s
e2e-windows (windows-2025, 22, npm, 5)	1m 16s
e2e-windows (windows-2025, 22, esbuild, 1)	1m 9s
e2e-windows (windows-2025, 22, esbuild, 0)	1m 9s
e2e-windows (windows-2025, 22, esbuild, 4)	1m 15s
e2e-windows (windows-2025, 22, esbuild, 2)	3m 12s
e2e-windows (windows-2025, 22, esbuild, 5)	1m 8s
e2e-windows (windows-2025, 22, esbuild, 3)	1m 14s
e2e-snapshots	1s
e2e	1s
e2e-package-managers	1s
	28m 37s

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