Make PersistentDict behave like an IdDict

[vchuravy]

As noted by @topolarity in #51993 (comment)

julia> x = Int64[0];

julia> d = Base.PersistentDict(x => false, [1] => true);

julia> x[1] = 1

julia> d[x]
true

I was already considering doing hash(sv::ScopedValue) = objectid(sv), but as cody showed this is a general issue,
The current behaviour is consistent with Dict but not with ImmutableDict (which PersistentDict is a close cousin off).

[Keno]

I think this makes sense, but I do wonder whether we shouldn't parameterize this on what hash/equality you want. I think both ===/objectid and isequal/Base.hash make sense, so it should probably be up to the user (with the ScopedValue use case using ===).

[Keno]

I'd like to finish #51993 if possible, so why don't we go ahead with this and then we can generalize in the future.