Implements the strong mode proposal's restrictions on the syntax of the
switch statement. Also fixes a minor bug with empty statements in strong
mode and improves StrongUndefinedArrow parser synch tests.
BUG=v8:3956
LOG=N
Review URL: https://codereview.chromium.org/1084983002
Cr-Commit-Position: refs/heads/master@{#27885}
