Port e920b2e3

Original Commit Message:

    - Debugger stepping assumes that the pc points to the instruction
      that should get executed next, so we need to increment it when
      we hit a stop or a bkpt instruction or else we'll end up in an
      infinite loop.
    - The "break" and the "stop unstop" command write into code space, so
      they need to temporarily make code space writable or else they
      just crash. (Note that this doesn't work for embedded builtins.)

R=neis@chromium.org, joransiu@ca.ibm.com, jyan@ca.ibm.com, michael_dawson@ca.ibm.com
BUG=
LOG=N

Change-Id: I1a9507f621c83dd94f2de230f7c75bc1fee95dd0
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2031204Reviewed-by: Georg Neis <neis@chromium.org>
Commit-Queue: Milad Farazmand <miladfar@ca.ibm.com>
Cr-Commit-Position: refs/heads/master@{#66057}