Re-enable CMake Build types MinSizeRel and RelWithDebInfo

[ptheywood]

We currently explicitly set the only build types to Release and Debug in our CMake, removing the other default options of MinSizeRel (-O2) and RelWithDebInfo (-O2 -gopt).

This was to match FLAME GPU 1's available build modes (which also included a profile build mode, but this was removed due to a lack of use).

These can be very useful in some cases (i.e. when there are bugs in release builds only), and as a CMake project it probably makes sense to keep them. They also cause no harm, other than 2 other options being present in drop down boxes in the CMake GUI and Visual Studio GUI.

This will be a simple change if it's agreed to re-enable them, and simply removing a couple of lines of CMake in common.cmake (both here and in the vis repo)