Fix compiler errors for UnitTestMapperGLFW

This file was creating a C array using the size of an array handle. Generally, you cannot create a C array of a static size with a variable created at runtime. Apparently some compilers were able to trace back to fact that the array handle was a given size and used that, but not all compilers can do this. To get around the problem, just use a std::vector, which allows the data to be dynamically allocated.