Add a few more extensions we support, and some more we never will

* There are a handful of ARB and EXT extensions left that aren't in either
  the list of supported, or will-never support. These are ones that I want
  to support but haven't written the code for.

renderdoc/driver/gl/gl_common.cpp

@@ -79,6 +79,7 @@ void DoVendorChecks(const GLHookSet &gl, GLWindowingData context)
 			EXT_CHECK(ARB_enhanced_layouts);
 			EXT_CHECK(EXT_polygon_offset_clamp);
 			EXT_CHECK(KHR_blend_equation_advanced_coherent);
+			EXT_CHECK(EXT_raster_multisample);
 
 #undef EXT_CHECK
 		}