[release/10.0] Fix for persisting null optional complex property with default values

[Copilot]

Port of #37944
Fixes #37890

Description
When optional complex properties transition from non-null to null with default-valued properties, those default values were not being tracked and therefore not set to null in the database. This is the inverse scenario of the fix in #37664.

Customer impact
Silent failure to persist null values leading to data corruption; no workaround known.

How found
3 user reports on 10.0.3

Regression
No. Optional complex properties were introduced in EF 10.

Testing
Test added

Risk
Low — single condition removed; quirk added.

[Copilot]

Pull request overview

Ports a fix into release/10.0 for snapshot change tracking of optional complex properties when transitioning from non-null (with all default-valued inner properties) to null, ensuring the null is detected and persisted, with an AppContext quirk switch to restore the previous behavior if needed.

Changes:

• Update ChangeDetector.DetectComplexPropertyChange to mark inner complex properties modified on both null→non-null and non-null→null transitions (with opt-out quirk switch).
• Add a new specification test covering non-null(defaults)→null persistence for an optional multi-property complex type.
• Skip the new test for providers/configurations where it’s not supported (InMemory; SqlServer proxies/notification tracking).

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
src/EFCore/ChangeTracking/Internal/ChangeDetector.cs	Extends complex-property null-transition detection; adds Microsoft.EntityFrameworkCore.Issue37890 quirk switch to restore prior behavior.
test/EFCore.Specification.Tests/ComplexTypesTrackingTestBase.cs	Adds coverage for persisting non-null(defaults)→null on an optional complex property with multiple properties.
test/EFCore.InMemory.FunctionalTests/ComplexTypesTrackingInMemoryTest.cs	Skips the new test due to existing InMemory complex-type limitations (#31464).
test/EFCore.SqlServer.FunctionalTests/ComplexTypesTrackingSqlServerTest.cs	Skips the new test for the proxies/notification tracking variant (#36175).

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[AndriySvyryd]

@copilot Update progress using the servicing template from the servicing pr skill

[Copilot]

@copilot Update progress using the servicing template from the servicing pr skill

Updated the PR description to follow the servicing template with all required sections (Description, Customer impact, How found, Regression, Testing, Risk).

[artl93]

Approved. New scenario, customer reported.