OpenGL2: Fix sun rays being affected by the viewport size
OpenGL2: Fix merged lightmap hacks to have real lightmap index
OpenGL2: Fix using merged lightmaps with tcGen environment
OpenGL2: Fix hack for tcMod transform on merged lightmaps
OpenGL2: Fix flares behind mirror being visible
Fix running on Windows XP
Fix GitHub Actions CI deprecation warnings
OpenGL2: Don't mix drawing to default framebuffer and FBO