vkd3d-shader/hlsl: Error out when an output semantic is used more than once.

The use of the hlsl_semantic.reported_duplicated_output_next_index field
allows reporting multiple overlapping indexes, such as in the following
vertex shader:

    void main(out float1x3 x : OVERLAP0, out float1x3 y : OVERLAP1)
    {
        x = float3(1.0, 2.0, 3.2);
        y = float3(5.0, 6.0, 5.0);
    }

    apple.hlsl:1:41: E5013: Output semantic "OVERLAP1" is used multiple times.
    apple.hlsl:1:13: First use of "OVERLAP1" is here.
    apple.hlsl:1:41: E5013: Output semantic "OVERLAP2" is used multiple times.
    apple.hlsl:1:13: First use of "OVERLAP2" is here.

While at the same time avoiding reporting overlaps more than once for
large arrays:

    struct apple
    {
        float2 p : sv_position;
    };

    void main(out apple aps[4])
    {
    }

    apple.hlsl:3:8: E5013: Output semantic "sv_position0" is used multiple times.
    apple.hlsl:3:8: First use of "sv_position0" is here.

libs/vkd3d-shader/hlsl.y

@@ -4784,6 +4784,7 @@ semantic:
             $$.name = $2;
             $$.index = atoi(p);
             $$.reported_missing = false;
+            $$.reported_duplicated_output_next_index = 0;
             *p = 0;
         }