This is a reland of f605d778

Adds a GC safe (using handles) and unsafe versions of the iterator.

V8HeapExplorer needs an unsafe one, since it does not allow the
creation of handles.

Original change's description:
> [runtime] Adds LocalNameIterator
>
> ScopeInfo will contain either inlined (array) local names or
> a hash table (names => index) containing the local names.
>
> We abstract iteration with LocalNameIterator and remove
> ContextLocalName since accessing a local name by index in
> the hash table would be expensive.
>
> This CL only implements the iterator for the array.
>
> Bug: v8:12315
> Change-Id: I2c62802652fca1cf47815ce8768a3f7487f2c39f
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3386603
> Reviewed-by: Toon Verwaest <verwaest@chromium.org>
> Commit-Queue: Victor Gomes <victorgomes@chromium.org>
> Cr-Commit-Position: refs/heads/main@{#78623}

Bug: v8:12315
Change-Id: I6288a08b9c342cd3a9cabcb621c40bb44c08c9c4
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/3394706Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Commit-Queue: Victor Gomes <victorgomes@chromium.org>
Cr-Commit-Position: refs/heads/main@{#78653}