Added unary expressions to semcheck and codegen.

test/codegen/unary.golden

@@ -0,0 +1,10 @@
+float4 vs_vs_main(float3 position : POSITION) : SV_POSITION
+{
+    return float4(position.x, position.y, position.z, 1.0f);
+}
+
+float4 ps_ps_main(float4 position : SV_POSITION) : SV_TARGET
+{
+    return float4(0.5f, -1, 0, 1);
+}
+