In this CL I remove the isolate from signatures of ExternalReference
accessor functions where the isolate is not used. The uses of the
isolate were already removed in previous CLs.

Changes:
* I split the ExternalReference list in external-reference.h into
those which need the isolate for initialization and those which do not.

* I removed the public constructors and replaced them by
  ExternalReference::Create(). The reason is to separate external
  creation more clearly from internal creation, because externally
  created ExternalReferences sometimes need redirection, whereas
  internally created ExternalReferences are just stored as they are.
  In addition, by removing the isolate from the signature of the
  public constructors, they suddenly exactly matched the interal
  constructor.

* Replace all uses of the public constructors with
  ExternalReference::Create().

* Remove the isolate from all call sites where necessary.


This is a step towards making WebAssembly compilation independent of
the isolate.

Bug: v8:7570
R=mstarzinger@chromium.org

Cq-Include-Trybots: luci.v8.try:v8_linux_noi18n_rel_ng
Change-Id: I14f511fc6acc50ab2d6a6641299f5ddbeabef0da
Reviewed-on: https://chromium-review.googlesource.com/1018982
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52768}