Complete merging of loads and converts

We still have a lot of load(exp).convert(type) style expressions in CodeGenerator. They generate unnecessary static conversion code, e.g.

    invokedynamic dyn:call(Object;Object;String;)Object;
    invokestatic JSType.toBoolean(Object;)Z

instead of the more natural

    invokedynamic dyn:call(Object;Object;String;)Z

These remaining expressions should be changed to load(exp, type).