Evaluation order for binary operators can be improved

JDK-8026137 fixed evaluation order to conform to the ECMA specification, but there are more cases where we can over-go strict order:

 - when loading right hand side from a local slot
 - when right hand side is a unary/binary/ternary operator whose children have no side effects
 - when left hand side already is JS-primitive or does not have to be converted to JS-primitive (already partially implemented)

Also, currently string is treated as object type while it is a primitive type as far as ECMA/JS is concerned.