Allow mapping arbitrary IEnumerables to arrays

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dotnet/efcore#29427 is enabling primitive collection support in EF, and we're implementing that via PostgreSQL arrays. Arrays have been supported in the PG provider for a long while, but was restricted to arrays and List<T>. Since it has been decided on the EF side that we should allow mapping any IEnumerable to a primitive collection in the database, the same should be done on the PG side as well.

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Note: restricting support to IList for now, because of complexities around change tracking (comparison over non-IList is problematic).