Bump version to "v21.0.0-rc.1" with changelog. #9658

Job	Run time
lint	2m 30s
build-e2e-windows-subset	6m 46s
analyze	5s
build	6m 32s
test	3m 9s
e2e-package-managers (ubuntu-latest, 22, yarn, 1)	5m 50s
e2e-package-managers (ubuntu-latest, 22, pnpm, 0)	6m 11s
e2e-package-managers (ubuntu-latest, 22, yarn, 0)	8m 4s
e2e-package-managers (ubuntu-latest, 22, pnpm, 2)	5m 50s
e2e-package-managers (ubuntu-latest, 22, yarn, 2)	7m 24s
e2e-package-managers (ubuntu-latest, 22, pnpm, 1)	4m 59s
e2e (ubuntu-latest, 22, npm, 1)	12m 20s
e2e (ubuntu-latest, 22, npm, 2)	11m 23s
e2e (ubuntu-latest, 22, npm, 0)	11m 31s
e2e (ubuntu-latest, 22, npm, 3)	8m 7s
e2e (ubuntu-latest, 22, npm, 5)	10m 36s
e2e (ubuntu-latest, 22, esbuild, 0)	7m 57s
e2e (ubuntu-latest, 22, esbuild, 3)	7m 26s
e2e (ubuntu-latest, 22, esbuild, 2)	8m 47s
e2e (ubuntu-latest, 22, esbuild, 1)	10m 3s
e2e (ubuntu-latest, 22, esbuild, 4)	6m 28s
e2e (ubuntu-latest, 22, esbuild, 5)	7m 10s
e2e (ubuntu-latest, 22, npm, 4)	8m 48s
e2e-snapshots	0s
e2e-windows-subset	4m 47s
	2h 52m 43s

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