Makes ExternalRefEncoder work even if no isolate is available,
by separating V8 builtin external references from isolate dependent ones,
and making the first set available without providing an isolate.

This is used when disassembling external references in wasm functions.

Bug: v8:11373
Change-Id: I9a177618185a6e5612182bcb02be7cc1978e8f34
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2799511Reviewed-by: Clemens Backes <clemensb@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Reviewed-by: Zhi An Ng <zhin@chromium.org>
Commit-Queue: Daan de Graaf <daagra@google.com>
Cr-Commit-Position: refs/heads/master@{#74025}