HLSL: phase 2b: add l-value operator[] for RWTexture/RWBuffer

This commit adds l-value support for RW texture and buffer objects.
Supported are:

- pre and post inc/decrement
- function out parameters
- op-assignments, such as *=, +-, etc.
- result values from op-assignments.  e.g, val=(MyRwTex[loc] *= 2);

Not supported are:
- Function inout parameters
- multiple post-inc/decrement operators.  E.g, MyRWTex[loc]++++;

hlsl/hlslParseHelper.h

@@ -81,7 +81,7 @@ public:
     void decomposeSampleMethods(const TSourceLoc&, TIntermTyped*& node, TIntermNode* arguments);
     TIntermTyped* handleLengthMethod(const TSourceLoc&, TFunction*, TIntermNode*);
     void addInputArgumentConversions(const TFunction&, TIntermNode*&) const;
-    TIntermTyped* addOutputArgumentConversions(const TFunction&, TIntermAggregate&) const;
+    TIntermTyped* addOutputArgumentConversions(const TFunction&, TIntermAggregate&);
     void builtInOpCheck(const TSourceLoc&, const TFunction&, TIntermOperator&);
     TFunction* handleConstructorCall(const TSourceLoc&, const TType&);
     void handleSemantic(TSourceLoc, TQualifier&, const TString& semantic);
@@ -152,6 +152,9 @@ public:
     void pushSwitchSequence(TIntermSequence* sequence) { switchSequenceStack.push_back(sequence); }
     void popSwitchSequence() { switchSequenceStack.pop_back(); }
 
+    // Apply L-value conversions.  E.g, turning a write to a RWTexture into an ImageStore.
+    TIntermTyped* handleLvalue(const TSourceLoc&, const char* op, TIntermTyped* node);
+
 protected:
     void inheritGlobalDefaults(TQualifier& dst) const;
     TVariable* makeInternalVariable(const char* name, const TType&) const;
@@ -161,6 +164,9 @@ protected:
     TIntermTyped* convertInitializerList(const TSourceLoc&, const TType&, TIntermTyped* initializer);
     TOperator mapAtomicOp(const TSourceLoc& loc, TOperator op, bool isImage);
 
+    // Return true if this node requires L-value conversion (e.g, to an imageStore).
+    bool shouldConvertLValue(const TIntermNode*) const;
+
     // Array and struct flattening
     bool shouldFlatten(const TType& type) const { return shouldFlattenIO(type) || shouldFlattenUniform(type); }
     TIntermTyped* flattenAccess(TIntermTyped* base, int member);