Add --hlsl-dx-position-w option

This reciprocates the w component of SV_Position in HLSL fragment shaders
to provide DirectX compatibility for HLSL shaders in Vulkan.

Fixes #2244

Test/hlsl.w-recip.frag

@@ -0,0 +1,12 @@
+float4 AmbientColor = float4(1, 0.5, 0, 1);
+float4 AmbientColor2 = float4(0.5, 1, 0, 0);
+
+float4 main(float4 vpos : SV_POSITION) : SV_TARGET
+{
+    float4 vpos_t = float4(vpos.xyz, 1 / vpos.w);
+    if (vpos_t.x < 400)
+        return AmbientColor;
+    else
+        return AmbientColor2;
+}
+