In particular, recognize builtins' values accesses and direct accesses
to external reference values. For example:

  REX.W leaq rax,[r13+0x47a0]
  REX.W leaq rbx,[r13+0x80b0]

turns into

  REX.W leaq rax,[r13+0x47a0] (builtin (RecordWrite))
  REX.W leaq rbx,[r13+0x80b0] (external value (Isolate::context_address))

This CL also extends the via-root-register-accessible region to the
whole Isolate object.

Bug: v8:8238
Change-Id: I218d8589690579919cfa01b2f3c3094af0e73c51
Reviewed-on: https://chromium-review.googlesource.com/1251550
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56332}