- Implemented GL_EXT_color_buffer_float.
- Removed duplicate glRenderbufferStorageMultisample implementation.
- Refactored internalformat validation.
- Removed GL_R11F_G11F_B10F as renderable format. OpenGL ES 3.0 only supports
  this as a texture format.

Change-Id: I83ce8225c1b310006f5ce983349ea8cb8b2f7c29
Reviewed-on: https://swiftshader-review.googlesource.com/9048Tested-by: Nicolas Capens <capn@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>