cmExperimental: recycle the C++ modules API UUID

Help/dev/experimental.rst

Source/cmExperimental.cxx

Tests/RunCMake/CXXModules/CMakeLists.txt

Tests/RunCMake/CXXModules/examples/cxx-modules-rules.cmake

...amples/export-bmi-and-interface-build/test/CMakeLists.txt

...ples/export-bmi-and-interface-install/test/CMakeLists.txt

...dules/examples/export-interface-build/test/CMakeLists.txt

...les/examples/export-interface-install/test/CMakeLists.txt

.../export-interface-no-properties-build/test/CMakeLists.txt

...xport-interface-no-properties-install/test/CMakeLists.txt

...XXModules/examples/export-usage-build/test/CMakeLists.txt

...Modules/examples/export-usage-install/test/CMakeLists.txt

.../target_sources/FileSetDefaultWrongTypeExperimental.cmake

...unCMake/target_sources/FileSetWrongTypeExperimental.cmake