While this is mostly a mechanical change to enable re-visiting macros for
inlining, it has a few user-facing effects:

- Labels and (variables, parameters, local constants) are handled separately,
  so they do not shadow each other.
- A local variable or constant is not bound in its initializer.
  This allows code like:

  const x = 5;
  {
    const x = x + 1;
  }


Bug: v8:7793
Change-Id: I968e1f93d92689737362c803342a797d312e95cd
Reviewed-on: https://chromium-review.googlesource.com/c/1276628
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Reviewed-by: Daniel Clifford <danno@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56649}