Enables the Scanner to provide a better error message when errors occur
in escape sequences, numbers, strings, etc.

BUG=v8:4829, v8:3230
LOG=N
R=adamk@chromium.org, littledan@chromium.org

Review URL: https://codereview.chromium.org/1793913002

Cr-Commit-Position: refs/heads/master@{#34966}