Half-float formats are renderable due to GL_EXT_color_buffer_half_float.

Change-Id: I4c3716f578cb4a5dd32f2b22265df4263e9834cc
Reviewed-on: https://swiftshader-review.googlesource.com/5127Tested-by: Nicolas Capens <capn@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>