Break out long case-block into its own function. #4124

Job	Run time
ClangTidy	1h 14m 41s
KytheVerification	0s
KytheXrefs	0s
MacOsBuild	2m 42s
x86_64 test	3m 18s
MacOsBuildDevTools	4m 24s
Generate Build matrix	4s
arm64 test	12m 9s
PrepareVSPlugin	2m 6s
x86_64 test-nortti	3m 25s
VerifyFormatting	1m 35s
WindowsBuild	5m 20s
x86_64 test-c++20	3m 24s
x86_64 test-c++23	3m 41s
x86_64 smoke-test	8m 40s
arm64 smoke-test	11m 4s
x86_64 asan	5m 28s
x86_64 asan-clang	4m 56s
x86_64 compile	2m 59s
arm64 compile	3m 44s
x86_64 compile-clang	2m 43s
arm64 compile-clang	3m 50s
x86_64 compile-static	2m 40s
arm64 compile-static	3m 44s
x86_64 compile-static-clang	2m 41s
arm64 compile-static-clang	4m 1s
x86_64 coverage	15m 27s
x86_64 clean	6m 10s
arm64 clean	7m 2s
Build ·${{ matrix.arch }}:${{ matrix.os }}:${{ matrix.ver }}${{ (((matrix.link == 'static') && ':static') \|\| '') }}	0s
Build and deploy GitHub pages	8s
📦 Release	0s
	3h 22m 6s

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