vkd3d-shader/spirv: Avoid emitting duplicate built-in inputs in spirv_compiler_emit_input().

This works around an issue introduced by commit
66cb2815f0. SV_PRIMITIVE_ID inputs in
geometry shaders use VKD3DSPR_PRIMID registers, and we create the
corresponding SPIR-V inputs using spirv_compiler_emit_io_register().
Unfortunately we also have an input signature element for the same
input, and simply creating another PrimitiveId input would run into
VUID-StandaloneSpirv-OpEntryPoint-09658.

Before the commit mentioned above, we'd use DCL_INPUT instructions to
emit input declarations, and these would help to distinguish whether
VKD3DSPR_INPUT or VKD3DSPR_PRIMID registers were used for primitive ID
inputs. Note that we can't simply ignore input signature element with
SIGNATURE_TARGET_LOCATION_UNUSED; the DXIL parser emits SV_SAMPLE_INDEX
inputs with that target location, but does require them to use a
VKD3DSPR_INPUT register.

libs/vkd3d-shader/vkd3d_shader_private.h

@@ -1023,6 +1023,20 @@ static inline bool vsir_register_is_descriptor(const struct vkd3d_shader_registe
     }
 }
 
+static inline enum vkd3d_shader_register_type vsir_register_type_from_sysval_input(
+        enum vkd3d_shader_sysval_semantic sysval)
+{
+    switch (sysval)
+    {
+        case VKD3D_SHADER_SV_PRIMITIVE_ID:
+            return VKD3DSPR_PRIMID;
+        case VKD3D_SHADER_SV_COVERAGE:
+            return VKD3DSPR_COVERAGE;
+        default:
+            return VKD3DSPR_INPUT;
+    }
+}
+
 struct vkd3d_shader_dst_param
 {
     struct vkd3d_shader_register reg;