Move getConflictingAltSubsets calculation, reduce its usage #1050

Job	Run time
cpp-lib-build (macos-11, clang, ON)	9m 26s
cpp-lib-build (macos-11, clang, OFF)	10m 41s
build (macos-11, tool)	1m 58s
build (macos-11, cpp)	43m 53s
cpp-lib-build (macos-11, gcc, ON)	9m 48s
cpp-lib-build (macos-11, gcc, OFF)	11m 24s
build (macos-11, csharp)	18m 10s
cpp-lib-build (ubuntu-20.04, clang, ON)	3m 23s
build (macos-11, dart)	8m 24s
build (macos-11, go)	4m 32s
cpp-lib-build (ubuntu-20.04, clang, OFF)	3m 23s
cpp-lib-build (ubuntu-20.04, gcc, ON)	4m 27s
cpp-lib-build (ubuntu-20.04, gcc, OFF)	5m 13s
cpp-lib-build (windows-2022, clang, ON)	4m 33s
cpp-lib-build (windows-2022, clang, OFF)	5m 36s
cpp-lib-build (windows-2022, cl)	4m 45s
build (macos-11, java)	3m 19s
build (macos-11, javascript)	6m 11s
build (macos-11, typescript)	24m 18s
build (macos-11, php)	2m 25s
build (macos-11, python3)	2m 11s
build (ubuntu-20.04, tool)	1m 9s
build (ubuntu-20.04, cpp)	17m 23s
build (ubuntu-20.04, csharp)	5m 17s
build (ubuntu-20.04, dart)	3m 47s
build (ubuntu-20.04, go)	2m 23s
build (ubuntu-20.04, java)	1m 14s
build (ubuntu-20.04, javascript)	1m 32s
build (ubuntu-20.04, typescript)	10m 3s
build (ubuntu-20.04, php)	1m 56s
build (ubuntu-20.04, python3)	1m 15s
build (windows-2022, tool)	1m 43s
build (windows-2022, cpp)	22m 27s
build (windows-2022, csharp)	6m 49s
build (windows-2022, dart)	4m 12s
build (windows-2022, go)	5m 26s
build (windows-2022, java)	1m 55s
build (windows-2022, javascript)	2m 14s
build (windows-2022, typescript)	21m 33s
build (windows-2022, php)	2m 41s
build (windows-2022, python3)	1m 41s
	5h 4m 40s

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