vkd3d-shader/glsl: Invert gl_FragCoord w.

Approved-by: Henri Verbeet (@hverbeet)
Merge-Request: https://gitlab.winehq.org/wine/vkd3d/-/merge_requests/1441

tests/hlsl/pixel-position.shader_test

@@ -0,0 +1,32 @@
+[vb 0]
+-1.0 -1.0 0.1 1.2
+-1.0  1.0 0.1 2.0
+ 1.0 -1.0 0.7 1.2
+ 1.0  1.0 0.7 2.0
+
+[input layout]
+0 r32g32b32a32-float POSITION
+
+[vertex shader]
+float4 main(float4 pos : POSITION) : sv_position
+{
+    return pos;
+}
+
+[pixel shader fail(sm<4) todo(sm<4)]
+float4 main(float4 pos : sv_position) : sv_target
+{
+    return pos;
+}
+
+[test]
+clear rtv 0 0.0 0.0 0.0 0.0
+todo(msl) draw triangle strip 4
+probe ( 80, 140) rgba(  0.0,   0.0, 0.0,         0.0)
+probe ( 80, 420) rgba( 80.5, 420.5, 0.100678146, 1.229981) 192
+probe (180, 140) rgba(180.5, 140.5, 0.077760354, 1.918082) 192
+probe (180, 420) rgba(180.5, 420.5, 0.194427669, 1.229981) 192
+probe (460, 140) rgba(460.5, 140.5, 0.340260297, 1.918082) 192
+probe (460, 420) rgba(460.5, 420.5, 0.456926346, 1.229981) 192
+probe (560, 140) rgba(  0.0,   0.0, 0.0, 0.0)
+probe (560, 420) rgba(560.5, 420.5, 0.550675929, 1.229981) 192