Render targets with only a red or alpha component were getting swapped values within pixel quads at the edge of primitives. Also provide format mappings for GL_EXT_texture_rg. Change-Id: Ifb395039fb2958400ab36d5d184d7952d60fa9c6 Reviewed-on: https://swiftshader-review.googlesource.com/13268Reviewed-by: Alexis Hétu <sugoi@google.com> Tested-by: Nicolas Capens <nicolascapens@google.com>
