HLSL: Non-functional: Move partial flattened access into symbol node.

Lays the groundwork for fixing issue #954.

Partial flattenings were previously tracked through a stack of active subsets
in the parse context, but full functionality needs AST nodes to represent
this across time, removing the need for parsecontext tracking.

glslang/Include/intermediate.h

@@ -945,7 +945,11 @@ public:
     // per process threadPoolAllocator, then it causes increased memory usage per compile
     // it is essential to use "symbol = sym" to assign to symbol
     TIntermSymbol(int i, const TString& n, const TType& t)
-        : TIntermTyped(t), id(i), constSubtree(nullptr)
+        : TIntermTyped(t), id(i),
+#ifdef ENABLE_HLSL
+        flattenSubset(-1),
+#endif
+        constSubtree(nullptr)
           { name = n; }
     virtual int getId() const { return id; }
     virtual const TString& getName() const { return name; }
@@ -956,9 +960,16 @@ public:
     const TConstUnionArray& getConstArray() const { return constArray; }
     void setConstSubtree(TIntermTyped* subtree) { constSubtree = subtree; }
     TIntermTyped* getConstSubtree() const { return constSubtree; }
+#ifdef ENABLE_HLSL
+    void setFlattenSubset(int subset) { flattenSubset = subset; }
+    int getFlattenSubset() const { return flattenSubset; } // -1 means full object
+#endif
 
 protected:
     int id;                      // the unique id of the symbol this node represents
+#ifdef ENABLE_HLSL
+    int flattenSubset;           // how deeply the flattened object rooted at id has been dereferenced
+#endif
     TString name;                // the name of the symbol this node represents
     TConstUnionArray constArray; // if the symbol is a front-end compile-time constant, this is its value
     TIntermTyped* constSubtree;