repl: refactor `LineParser` implementation

Move the core logic from `LineParser` should fail handling into the
recoverable error check for the REPL default eval.

PR-URL: https://github.com/nodejs/node/pull/6171


Reviewed-By: James M Snell <jasnell@gmail.com>
Reviewed-By: Michaël Zasso <targos@protonmail.com>