Fix 'ordinal -1 is invalid' crash when a nested JSON complex sub-collection grows

[Copilot]

An entity with a JSON-mapped complex property whose nested collection items define 2+ sub-collections would throw on save when one sub-collection grew between load and save:

System.InvalidOperationException: Complex entry original ordinal '-1' is invalid for property
'...XDeepItem[]XInnerEntry.Inner' as it's outside of the collection of length '1'.

Root cause

InternalEntryBase.SetPropertyModified's recurse loop forced every flattened complex-collection element — including Added ones — to Modified/Unchanged. For a newly-grown element (an Added entry, whose original ordinal is legitimately -1), InternalComplexEntry.SetEntityState then ran ValidateOrdinal(original: true), which throws.

Changes

• InternalEntryBase.SetPropertyModified: skip Added complex entries in the recurse loop, mirroring the guard already present in the bulk InternalComplexCollectionEntry.SetEntityState. Their state is left as computed by change detection.

  foreach (var complexEntry in GetFlattenedComplexEntries())
  {
      if (!UseOldBehavior38299
          && complexEntry.EntityState is EntityState.Added)
      {
          continue;
      }
  
      complexEntry.SetEntityState(newElementState, modifyProperties: true);
  }

• Quirk switch: gated behind Microsoft.EntityFrameworkCore.Issue38299 (UseOldBehavior38299), consistent with servicing precedent (Can't change state of entity with complex collection #37724/Deleting an item from a ComplexCollection, that contains an array results in Error #37585).

• Tests: added Grow_nested_sub_collection_in_complex_property_mapped_to_json to the relational ComplexCollectionJsonUpdateTestBase (new WidgetWithDeepJson model: ToJson → wrapper → item collection → item with two sub-collections), plus the SQLite override with SQL baseline.

Reviewer note

The bug's reproduction is sensitive to the global complex-collection index ordering (name/structure dependent). The fix is verified end-to-end against a standalone repro matching the issue's model in both directions (crashes without the guard, persists the grown collection with it). The added harness test exercises the grow-and-replace path; a reviewer may want to consider strengthening it (e.g. adding the second JSON column noted in the issue) so it fails hard without the fix rather than serving primarily as a feature test.