data: parse variable usage

* Implemented functions for parsing usages of fields and global variables in ASTBodyVisitor and ASTVisitor.
* Storage adds TokenLocatons and Edges for usages.
* Added tests for parsing usage of fields and global variables.

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src/lib/data/parser/cxx/ASTBodyVisitor.h

@@ -14,6 +14,8 @@ public:
 	void VisitChildren(clang::Stmt* stmt);
 	void VisitCallExpr(clang::CallExpr* expr);
 	void VisitCXXConstructExpr(clang::CXXConstructExpr* expr);
+	void VisitMemberExpr(clang::make_ptr<clang::MemberExpr>::type expr);
+	void VisitDeclRefExpr(clang::make_ptr<clang::DeclRefExpr>::type expr);
 
 private:
 	ASTBodyVisitorClient* m_client;