To make async/await catch prediction work well, this patch regularizes
the exception events sent to DevTools from various places in the Promise
lifecycle. The core is that there should be an exception event when the
rejection first starts, rather than when it is propagated.

- Several cases within Promise code which propagate errors are
  modified to not trigger a new ExceptionEvent in that case, such
  as .then on a rejected Promise and returning a rejected Promise
  from .then, as well as Promise.race and Promise.all.
- Make Promise.reject() create an ExceptionEvent, subject to catch
  prediction based on the Promise stack. This is important
  so that, e.g., if "await Promise.reject()" will trigger a new
  throw (rather than a silent rethrow of something that never
  triggered an event in the first place).

BUG=v8:5167

Review-Url: https://codereview.chromium.org/2244003003
Cr-Commit-Position: refs/heads/master@{#38847}