Honor Where clauses on the inner source of GroupJoin

[snrnats]

Where predicates chained onto the inner IQueryable passed to GroupJoin were silently dropped during SQL compilation. They are now extracted from the inner source expression tree and applied to the inner CTE so filtering happens before the join.

Problem

Given a query like:

await session.Query<Customer>()
    .GroupJoin(
        session.Query<Order>().Where(o => o.Status == "Shipped"),
        c => c.Id,
        o => o.CustomerId,
        (c, orders) => new { c, orders })
    .SelectMany(x => x.orders, (x, o) => new { x.c.Name, o.Amount })
    .ToListAsync();

The Where(o => o.Status == "Shipped") was completely ignored — the inner CTE was built straight from Order storage with only the default tenant/soft-delete filters.

[jeremydmiller]

@snrnats