Adjusting code interface

glslang/include/intermediate.h -> Add a new interface to set TIntermBranch's expression.

glslang/include/Types.h -> Add interface to set Type's basicType and add interface to get basicType form a TSampler.

glslang/MachineIndependent/intermediate.cpp -> Part of the code in createConversion been encapsulating as a new function called buildConvertOp

glslang/MachineIndependent/localintermediate.h -> Export createConversion and
buildConvertOp as a public function

glslang/Public/ShaderLang.h -> Add interface to get shader object and shader source.

glslang/Include/intermediate.h

@@ -1185,6 +1185,7 @@ public:
     virtual void traverse(TIntermTraverser*);
     TOperator getFlowOp() const { return flowOp; }
     TIntermTyped* getExpression() const { return expression; }
+    void setExpression(TIntermTyped* pExpression) { expression = pExpression; }
 protected:
     TOperator flowOp;
     TIntermTyped* expression;