Implement support for FSAA in combination with post-processing (#15392)

- Actually it's MSAA I think, or perhaps the terms are equivalent
- I've made it fit into the existing Irrlicht architecture, but that has resulted in code duplication compared to my original "hacky" approach
- OpenGL 3.2+ and OpenGL ES 3.1+ are supported
- EDT_OPENGL3 is not required, EDT_OPENGL works too
- Helpful tutorial: https://learnopengl.com/Advanced-OpenGL/Anti-Aliasing, section "Off-screen MSAA"
- This may be rough around the edges, but in general it works

irr/src/COpenGLExtensionHandler.cpp

@@ -612,6 +612,8 @@ bool COpenGLExtensionHandler::queryFeature(E_VIDEO_DRIVER_FEATURE feature) const
 		return FeatureAvailable[IRR_ARB_seamless_cube_map];
 	case EVDF_DEPTH_CLAMP:
 		return FeatureAvailable[IRR_NV_depth_clamp] || FeatureAvailable[IRR_ARB_depth_clamp];
+	case EVDF_TEXTURE_MULTISAMPLE:
+		return (Version >= 302) || FeatureAvailable[IRR_ARB_texture_multisample];
 
 	default:
 		return false;