HLSL: cast bracket dereference index to int type if not.

HLSL can index arrays using operator[] with non-integer types, and
inserts a conversion to a uint if needed.

gtests/Hlsl.FromFile.cpp

@@ -171,6 +171,7 @@ INSTANTIATE_TEST_CASE_P(
         {"hlsl.logicalConvert.frag", "main"},
         {"hlsl.logical.unary.frag", "main"},
         {"hlsl.namespace.frag", "main"},
+        {"hlsl.nonint-index.frag", "main"},
         {"hlsl.matNx1.frag", "main"},
         {"hlsl.matrixSwizzle.vert", "ShaderFunction"},
         {"hlsl.mintypes.frag", "main"},