Update cmakelists to use system googletest if available. #170

Job	Run time
bazel-build (ubuntu-latest)	36s
bzlmod-build (ubuntu-latest)	35s
bazel-build (windows-latest)	4m 46s
cmake-build (ubuntu-latest, 11, static, Default Generator)	1m 8s
bzlmod-build (windows-latest)	5m 3s
bazel-build (macos-latest)	1m 57s
cmake-build (ubuntu-latest, 11, shared, Default Generator)	3m 43s
bzlmod-build (macos-latest)	2m 7s
cmake-build (ubuntu-latest, 17, static, Default Generator)	1m 9s
cmake-build (ubuntu-latest, 17, shared, Default Generator)	1m 27s
cmake-build (ubuntu-latest, 20, static, Default Generator)	1m 37s
cmake-build (ubuntu-latest, 20, shared, Default Generator)	1m 51s
cmake-build (windows-latest, 11, static, Default Generator)	8s
cmake-build (windows-latest, 11, static, MinGW Makefiles)	7s
cmake-build (windows-latest, 11, shared, Default Generator)	4s
cmake-build (windows-latest, 11, shared, MinGW Makefiles)	5s
cmake-build (windows-latest, 17, static, Default Generator)	7s
cmake-build (windows-latest, 17, static, MinGW Makefiles)	9s
cmake-build (windows-latest, 17, shared, Default Generator)	7s
cmake-build (windows-latest, 17, shared, MinGW Makefiles)	5s
cmake-build (windows-latest, 20, static, Default Generator)	8s
cmake-build (windows-latest, 20, static, MinGW Makefiles)	7s
cmake-build (windows-latest, 20, shared, Default Generator)	6s
cmake-build (windows-latest, 20, shared, MinGW Makefiles)	7s
cmake-build (macos-latest, 11, static, Default Generator)	4s
cmake-build (macos-latest, 17, static, Default Generator)	5s
cmake-build (macos-latest, 20, static, Default Generator)	12s
	27m 40s

Provide feedback