Allow projecting owned entities from tracking queries (without tracking them)

When an owned entity is projected without its owner from a tracking query, we current throw a non-suppressible error. We should instead generate a warning-as-error by default, allowing users to suppress it.

The is especially troublesome for Cosmos, where this makes it impossible to project a document fragment without explicitly stating AsNoTracking.

Note: do this for relational and Cosmos. Once this is done, the relationship projection tests can be considerably simplified - we can just suppress the warning and remove all the special handling.

/cc @AndriySvyryd