Add isolation smoke tests for C++ headers

[rdw-software]

Check your header filies by compiling them in isolation via a testMain.cpp that includes nothing but the header file under test. If it produces a compilation error, then something either needs to get included in the header file or forward declared. The process should be repeated for all header files in the project using a bottoms-up approach. This’ll help prevent random build break as the code base grows larger and code blocks are moved around.