HLSL: add optional position.Y inversion

Adds command line options:

   --invert-y
   --iy

(synonyms) which invert position.Y on vertex shader output.  Handles these cases:

* Direct single variable return
* Member of direct returned struct
* Single variable output parameter
* Member of struct output parameter

API:

    // Enables position.Y output negation in vertex shader
    void TShader::setInvertY(bool invert);

Fixes #1173

glslang/MachineIndependent/ShaderLang.cpp

@@ -1686,6 +1686,8 @@ void TShader::setShiftUavBinding(unsigned int base)     { setShiftBinding(EResUa
 void TShader::setShiftSsboBinding(unsigned int base)    { setShiftBinding(EResSsbo, base); }
 // Enables binding automapping using TIoMapper
 void TShader::setAutoMapBindings(bool map)              { intermediate->setAutoMapBindings(map); }
+// Enables position.Y output negation in vertex shader
+void TShader::setInvertY(bool invert)                   { intermediate->setInvertY(invert); }
 // Fragile: currently within one stage: simple auto-assignment of location
 void TShader::setAutoMapLocations(bool map)             { intermediate->setAutoMapLocations(map); }
 // See comment above TDefaultHlslIoMapper in iomapper.cpp:

glslang/MachineIndependent/localintermediate.h

@@ -224,6 +224,7 @@ public:
 #endif
         autoMapBindings(false),
         autoMapLocations(false),
+        invertY(false),
         flattenUniformArrays(false),
         useUnknownFormat(false),
         hlslOffsets(false),
@@ -317,6 +318,14 @@ public:
             processes.addProcess("auto-map-locations");
     }
     bool getAutoMapLocations() const { return autoMapLocations; }
+    void setInvertY(bool invert)
+    {
+        invertY = invert;
+        if (invertY)
+            processes.addProcess("invert-y");
+    }
+    bool getInvertY() const { return invertY; }
+
     void setFlattenUniformArrays(bool flatten)
     {
         flattenUniformArrays = flatten;
@@ -682,6 +691,7 @@ protected:
     std::vector<std::string> resourceSetBinding;
     bool autoMapBindings;
     bool autoMapLocations;
+    bool invertY;
     bool flattenUniformArrays;
     bool useUnknownFormat;
     bool hlslOffsets;

glslang/Public/ShaderLang.h

@@ -371,6 +371,7 @@ public:
     void setResourceSetBinding(const std::vector<std::string>& base);
     void setAutoMapBindings(bool map);
     void setAutoMapLocations(bool map);
+    void setInvertY(bool invert);
     void setHlslIoMapping(bool hlslIoMap);
     void setFlattenUniformArrays(bool flatten);
     void setNoStorageFormat(bool useUnknownFormat);