Fix floating-point color buffer support.

- 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/9048
Tested-by: Nicolas Capens <capn@google.com>
Reviewed-by: Alexis Hétu <sugoi@google.com>

src/Shader/PixelRoutine.cpp

diff --git a/src/Shader/PixelRoutine.cpp b/src/Shader/PixelRoutine.cpp
index d0650b0..16e4692 100644
--- a/src/Shader/PixelRoutine.cpp
+++ b/src/Shader/PixelRoutine.cpp
@@ -2543,7 +2543,7 @@
 			}
 
 			{
-				value = (state.targetFormat[index] == FORMAT_X32B32G32R32F) ? Float4(1.0f) : *Pointer<Float4>(buffer + 16, 16);
+				value = *Pointer<Float4>(buffer + 16, 16);
 
 				if(rgbaWriteMask != 0x0000000F)
 				{