Allow to add and delete dependents sharing a table

[AndriySvyryd]

Description

Modifications to a shared row will derive their state only from the main entry (the entry that isn't a dependent of any other entry in the row). If the main entry isn't present the row is assumed to be modified.
The principal entry is now not required to be in the same state as the dependent when saving changes to a shared row.

Fixes #17422
Fixes #17935

Customer impact

Allows to add and delete just the dependent entities when using table splitting.

Regression

No, optional dependents in table splitting is a new feature in 3.0

Risk

Medium, can impact other update scenarios.

[AndriySvyryd]

Ping. I'd like to push this in today.

[Neme12]

@AndriySvyryd

Regression

No, optional dependents in table splitting is a new feature in 3.0

Yes, this is a regression. The fact that they're optional is a new feature, but there's no way to opt out of that. In EF Core 2.2, I didn't use to get null for an owned entity, but now I do and there's nothing I can do to change that. Owned entity types are now completely unusable. 😞 Can you please consider backporting this to 3.0?

[AndriySvyryd]

@Neme12 There's no point fixing this in 3.0.x as that version would be released at the same time as 3.1.0. Use the preview version to unblock yourself.

[Neme12]

@AndriySvyryd But that requires not only a new version of EF Core, but also .NET Core which 1) has to be installed on the production server and 2) requires a new SDK (one that doesn't come with VS) which other devs won't want to install.

[AndriySvyryd]

@Neme12 EF Core 3.1 should work on .NET Core 3.0 and 3.0.x SDK

[Neme12]

@AndriySvyryd Thanks, it does! What confused me was the fact that I didn't get completion for that version number in VS. I filed an issue here: dotnet/ProjFileTools#66