Return true for IsModified on navigations pointing to Added or Deleted entities

[ajcvickers]

Fixes #16513

I investigated this some more and I now understand why this was labeled a bug. Collection navigations already have this behavior--that is, Deleted or Added related entities indicate that the navigation property is modified. So this change brings reference navigations inline, which I think is a bug. Nevertheless, I think it makes sense to document this as a breaking change.

[kipusoep]

Hi @ajcvickers, I just found this PR via #16513 and I'm afraid this does not work anymore in EFCore 7.0.9.
I have an entity, let's assume it's called MainEntity, which has an owned entity property called OwnedEntity. When I assign a newly constructed object to the OwnedEntity property, the MainEntity is not marked as modified.
Example:

class MainEntity
{
    public OwnedEntity OwnedEntity { get; set; }
}

[Owned]
class OwnedEntity
{
    // Some properties
}

var mainEntity = await _context.MainEntities.SingleOrDefaultAsync(x => x.Id == 1);
mainEntity.OwnedEntity = new OwnedEntity {
    // Some properties
};
var state = _context.Entry(mainEntity).State;

// state == Unchanged

This should not be the case right?

[kipusoep]

Hmm my bad, I didn't notice this was only for the reference instead of the owner.