ExecuteUpdate: allow value tuples in setters for expressing row values

```c#
context.Blogs.ExecuteUpdate(s => s
.SetProperty(b => ValueTuple.Create(b.Title, b.Content), b => /* some subquery returning two values */);
```

This is important for performance, since the subquery runs only once and returns two values; otherwise the two properties need to be set separately, causing the subquery to be evaluated twice (that's the current workaround).

IIRC this does not work on SQL Server which doesn't support row values very well, but is supported on almost all other databases, including SQLite.

Possibly depends on:

* [ ] #26822