Support nullable complex types with all optional properties for table splitting

[AndriySvyryd]

If all of the properties are optional then we need to query all of the columns to which they are mapped to determine whether the complex property should contain null. If it contains a nested complex property this needs to be repeated recursively. If any of the columns are shared (another property is mapped to it) they need to be excluded from the above.

Split from #31376

[cincuranet]

@AndriySvyryd Any reason this is not in Backlog?