Fix stencil+MSAA

True integer types don't support MSAA, so the blitter never had support
for MSAA on true integer types. In Vulkan, VK_FORMAT_S8_UINT is a UINT
format, so it's considered a true integer type, but it must still support
MSAA.

Added support for MSAA on true integer types in the blitter so fix all
related tests with SwANGLE:
dEQP-GLES3.functional.depth_stencil_clear.*
dEQP-GLES3.functional.fragment_ops.*
dEQP-GLES3.functional.rasterizer_discard.*

Bug: angleproject:4044
Change-Id: I8e04f434f0f671999aaef23cf24cc6684fd0fc16
Reviewed-on: https://swiftshader-review.googlesource.com/c/SwiftShader/+/37548
Presubmit-Ready: Alexis Hétu <sugoi@google.com>
Kokoro-Presubmit: kokoro <noreply+kokoro@google.com>
Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Antonio Maiorano <amaiorano@google.com>

src/Device/Blitter.cpp

@@ -1453,7 +1453,12 @@ namespace sw
 
 					if(hasConstantColorI)
 					{
-						write(constantColorI, d, state);
+						for(int s = 0; s < state.destSamples; s++)
+						{
+							write(constantColorI, d, state);
+
+							d += *Pointer<Int>(blit + OFFSET(BlitData, dSliceB));
+						}
 					}
 					else if(hasConstantColorF)
 					{
@@ -1479,7 +1484,12 @@ namespace sw
 
 						// When both formats are true integer types, we don't go to float to avoid losing precision
 						Int4 color = readInt4(s, state);
-						write(color, d, state);
+						for(int s = 0; s < state.destSamples; s++)
+						{
+							write(color, d, state);
+
+							d += *Pointer<Int>(blit + OFFSET(BlitData,dSliceB));
+						}
 					}
 					else
 					{