OpenGL linking error on Windows

[adazem009]

The library isn't linked against OpenGL which causes this error:

ld.exe: scratchcpp-render/src/libscratchcpp-render.a(renderedtarget.cpp.obj):renderedtarget:(.text+0x276c): undefined reference to `__imp_glReadPixels'

However, Qt is linked against OpenGL, so QOpenGLFunctions should be used instead of directly calling the functions.