HLSL: fix for flattening assignments from non-symbol R-values.

If a member-wise assignment from a non-flattened struct to a flattened struct sees a complex R-value
(not a symbol), it now creates a temporary to hold that value, to avoid repeating the R-value.
This avoids, e.g, duplicating a whole function call.  Also, it avoids re-using the AST node, making a
new one for each member inside the member loop.

The latter (re-use of AST node) was also an issue in the GetDimensions intrinsic decomposition,
so this PR fixes that one too.

glslang/MachineIndependent/Intermediate.cpp

@@ -73,6 +73,16 @@ TIntermSymbol* TIntermediate::addSymbol(int id, const TString& name, const TType
     return node;
 }
 
+TIntermSymbol* TIntermediate::addSymbol(const TIntermSymbol& intermSymbol)
+{
+    return addSymbol(intermSymbol.getId(),
+                     intermSymbol.getName(),
+                     intermSymbol.getType(),
+                     intermSymbol.getConstArray(),
+                     intermSymbol.getConstSubtree(),
+                     intermSymbol.getLoc());
+}
+
 TIntermSymbol* TIntermediate::addSymbol(const TVariable& variable)
 {
     glslang::TSourceLoc loc; // just a null location