Implement sRGB texture sampling.

Previously sRGB data was converted to linear space on upload. This
caused a loss of precision. This change performs the conversion after
texel lookup. Note that we had a code path for performing the
conversion after filtering, but that leads to failures in dEQP and
unacceptable darkening between texels.

Also, glTexSubImage calls can update sRGB textures using a format/type
combination with no indication of the color space, which caused an
unintentional conversion on upload. Likewise we were missing support
for an A2B10G10R10UI implementation format.

Change-Id: Ib10845f628fb2d1849e88d7a9350868cdec32fa2
Reviewed-on: https://swiftshader-review.googlesource.com/15068
Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>

src/Renderer/Sampler.cpp

diff --git a/src/Renderer/Sampler.cpp b/src/Renderer/Sampler.cpp
index 5862996..85448b9 100644
--- a/src/Renderer/Sampler.cpp
+++ b/src/Renderer/Sampler.cpp
@@ -96,7 +96,7 @@
 			state.addressingModeV = getAddressingModeV();
 			state.addressingModeW = getAddressingModeW();
 			state.mipmapFilter = mipmapFilter();
-			state.sRGB = sRGB && Surface::isSRGBreadable(externalTextureFormat);
+			state.sRGB = (sRGB && Surface::isSRGBreadable(externalTextureFormat)) || Surface::isSRGBformat(internalTextureFormat);
 			state.swizzleR = swizzleR;
 			state.swizzleG = swizzleG;
 			state.swizzleB = swizzleB;