[PATCH 0/1] MR179: vkd3d-shader/hlsl: Add support for ddx(), ddy() intrinsics.

[Ethan Lee (＠flibitijibibo)]

SPIR-V already handled DSX/DSY, so only D3DBC/TPF needed new case blocks.

You'll notice that there's no test for this one - in addition to being a pretty straightforward translation for all possible formats, this feature uses the render target width/height and I wasn't sure if there was a good way to ensure that the test would always make sense.

Instead, I did the test manually, and it's what you'd expect:

HLSL:
```
uniform float f;

float4 main() : sv_target
{
    float4 x = ddx(f);
    float4 y = ddy(f);
    return x + y;
}
```

D3DBC:
```
ps_3_0
mov r0.x, c0.x
dsx r1.x, r0.x
dsy r0.x, r0.x
mov r1.xyzw, r1.x
mov r0.xyzw, r0.x
add r0.xyzw, r1.xyzw, r0.xyzw
mov oC0.xyzw, r0.xyzw
```

DXBC-TPF:
```
ps_4_0
dcl_constantBuffer cb0[1], immediateIndexed
dcl_output o0.xyzw
dcl_temps 2
mov r0.x, cb0[0].x
dsx r0.y, r0.x
dsy r0.x, r0.x
mov r1.xyzw, r0.y
mov r0.xyzw, r0.x
add r0.xyzw, r1.xyzw, r0.xyzw
mov o0.xyzw, r0.xyzw
ret
```