This patch cleans up the Intl code by switching to using declared
accessors, rather than embedder fields, for holding references to
ICU objects. Additionally:
- Rename classes to be more similar to how other classes are named
- Make some unreachable paths into check-fails, rather than throwing
  JS exceptions
- Move some macros from objects-inl.h into object-macros.h, to allow
  the implementation here to not touch objects.h
- Some setup logic is moved from runtime-i18n.cc to i18n.cc.

This patch leaves type tags as they are; a future patch should move
from a special Intl type tagging system to object types as other system
objects use. Future patches should also move more logic to i18n.cc

BUG=v8:5402,v8:5751,v8:6057
CQ_INCLUDE_TRYBOTS=master.tryserver.v8:v8_linux_noi18n_rel_ng

Change-Id: Ia9cbb25cf8f52662e3deb15e64179d792c10842c
Reviewed-on: https://chromium-review.googlesource.com/479651
Commit-Queue: Daniel Ehrenberg <littledan@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#44804}