Split CMake identities: superproject and 'developer' #447

Job	Run time
windows_msvc_14_2 (msvc-14.2)	1s
posix-cmake-subdir (macos-13)	3m 40s
posix-cmake-subdir (ubuntu-24.04)	1m 32s
posix-cmake-subdir (ubuntu-22.04)	1m 19s
windows-cmake-subdir (windows-2022)	2m 51s
windows-cmake-install (windows-2019)	1s
windows_msvc_14_3 (msvc-14.3)	22m 57s
posix-cmake-subdir (macos-15)	1m 23s
windows-cmake-subdir (windows-2019)	1s
windows-cmake-install (windows-2022)	4m 17s
macos (clang, 20)	7m 43s
macos (clang, 17)	5m 54s
posix-cmake-subdir (macos-14)	1m 22s
ubuntu (gcc-14, 14)	7m 24s
ubuntu (gcc-14, 17)	7m 30s
posix-cmake-install (ubuntu-24.04)	1m 46s
ubuntu (clang-19, 20)	11m 23s
ubuntu (gcc-14, 20)	8m 3s
macos (clang, 14)	6m 50s
ubuntu (gcc-14, 23)	9m 0s
posix-cmake-install (macos-13)	3m 38s
posix-cmake-install (macos-14)	2m 41s
ubuntu (clang-19, 17)	10m 33s
ubuntu (clang-19, 14)	8m 29s
ubuntu (clang-19, 23)	11m 59s
posix-cmake-install (macos-15)	1m 38s
posix-cmake-install (ubuntu-22.04)	1m 42s
	2h 25m 37s

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