This refactors the instruction cache simulation to now be maintained
process-wide (as opposed to be per Isolate). It prepares for allowing
to share code between Isolates (e.g. WebAssembly or shared builtins)
while still allowing to simulate execution of such shared code.

R=clemensh@chromium.org

Change-Id: I5a6f083f4e32597565dc646f13b4445014c0daaa
Reviewed-on: https://chromium-review.googlesource.com/909130Reviewed-by: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#51219}