Fix CMake configuration and build of Phys/JetAccessoriesMC
Workin on !837 (merged), I realized that !795 (merged) re-introduced the subdirectory Phys/JetAccessoriesMC
which was removed from master before the CMake modernization (!793 (merged)).
The result is that the subdirectory was added with the old style CMake configuration, but not built because not explicitly added to the top level CMakeLists.txt
.
This MR modernizes the CMake configuration of Phys/JetAccessoriesMC
and adds it to the build.