This introduces a new syntax for identifiers and calls: modulename::foo.
Such a name is resolved by trying to find a module modulename in one of
the parent scopes and looking for foo there. So this roughly corresponds
to C++ qualified namespace lookup.

Bug: v8:7793
Change-Id: Iedc43e6ebe125cd74575cbbcbf990bbcc0155a1f
Reviewed-on: https://chromium-review.googlesource.com/c/1309818
Commit-Queue: Tobias Tebbi <tebbi@chromium.org>
Reviewed-by: Daniel Clifford <danno@chromium.org>
Cr-Commit-Position: refs/heads/master@{#57238}