During conflict lookup (for lexical variables and sloppy block function
hoisting), we cache the looked-up variable on the current scope if the
lookup goes through a ScopeInfo. However, for variable lookup during
scope analysis, we use the "entry point" as the cache.

Since both lookups can create Variables, this can cause us to create
duplicate variables, e.g. a duplicate function name variable in the
attached test.

Instead, for ScopeInfo conflict lookups we can cache the result on the
function's outer scope, which shoud be equivalent to the entry point.

As a (necessary) drive-by, we can terminate the lookup early if we find
a VAR with the same name, as we can safely assume that its existence
means that it doesn't conflict, which means that our variable can't
conflict either.

Bug: chromium:1026603
Change-Id: I19f80f65597ba6573ebe0b48aa5698f55e5c3ea1
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1928861
Commit-Queue: Leszek Swirski <leszeks@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Cr-Commit-Position: refs/heads/master@{#65138}