introduce interface for Operators during parsing

...nodes/src/com/oracle/truffle/r/nodes/RTruffleVisitor.java

...ser/src/com/oracle/truffle/r/parser/ParserGeneration.java

...acle.truffle.r.parser/src/com/oracle/truffle/r/parser/R.g

.../src/com/oracle/truffle/r/parser/ast/BinaryOperation.java

...parser/src/com/oracle/truffle/r/parser/ast/Operation.java

...r/src/com/oracle/truffle/r/parser/ast/UnaryOperation.java

...cle/truffle/r/parser/tools/EvaluatedArgumentsVisitor.java