Before this patch, the registers needed for bytecode dispatch in interpreter
handlers were inconsistently stored in the interpreter frame and/or kept in
values that remained live across calls.

After this patch, these registers are explicitly reloaded after calls, making it
possible to elide the spills of those registers before the call in many cases.

Some highlights from the CL:

* Added methods to the CSA and InterpreterAssembler to efficiently store and
  load Smis values and Smi interpreter registers on x64 without explicit
  tagging/untagging.

* Created Variables for all of the interpreter-internal values that need to be
  reloaded before bytecode dispatch at the end of an interpreter handler.

* The bytecode offset can be written out early in a handler by marking it
  has having a call along it's critical path. By moving this early in a
  handler, it becomes possible to use memory operands for pushes used to
  marshall parameters when making calls.

Change-Id: Icf8d7798789f88a4489e06a7092616bbbb881577
Reviewed-on: https://chromium-review.googlesource.com/442566
Commit-Queue: Daniel Clifford <danno@chromium.org>
Reviewed-by: Ross McIlroy <rmcilroy@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#43260}