This makes the code a little more specific to what's happening: There is only 1
global scope, and if there is one, we know its declarations are
info->scope()->declarations(). That means we don't need multiple
GlobalDeclarationsBuilders, and we don't need to cache partially serialized
versions of the declarations. One builder is enough, and we can simply walk
those declarations if there are any.

Additionally this CL drops unnecessary information passed into DeclareGlobals:
- Global functions always have the name on the shared function info, so we can
  drop the name.
- Due to lazy feedback vectors there's no point in trying to preinitialize
  global loads. Also this was only preinitializing global loads at the script
  level, not sub functions; without even checking whether the global load was
  used. It may actually have caused us to do more work and allocate more global
  load feedback slots than neccessary.

Change-Id: Ibbdd029abe5a39ba27f7fc9be84670c5d444d98d
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1997123
Commit-Queue: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Leszek Swirski <leszeks@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65725}