Unlike previous implementation where the 'continue' keyword was a feature of a return statement the keyword is now recognized as a part of expression. Error reporting was significantly improved.

--harmony-explicit-tailcalls option is now orthogonal to --harmony-tailcalls so we can test both modes at the same time.

This CL also adds %GetExceptionDetails(exception) that fetches hidden |start_pos| and |end_pos| values from the exception object.

BUG=v8:4915
LOG=N

Review-Url: https://codereview.chromium.org/1928203002
Cr-Commit-Position: refs/heads/master@{#36024}