Ignore overridden properties in JSON (de)serialization

[devsko]

Fixes#51165

Implicitly ignore properties that are overridden in a derived class but have a differing name set by JsonPropertyName.
This meets the current behavior of overridden properties with the same name or no JsonPropertyName at all.
Also fixes an issue with new virtual properties that were previously handled as override.

This seems to be a breaking change of the scenario described in #51165.

[ghost]

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Issue Details

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Fixes #51165

Implicitly ignore properties that are overridden in a derived class but have a differing name set by JsonPropertyName.
This meets the current behavior of overridden properties with the same name or no JsonPropertyName at all.

Author:	devsko
Assignees:	-
Labels:	area-System.Text.Json
Milestone:	-

[ericstj]

It's not clear to me if there was a conclusion on expected behavior here. We should get that before opening the PR. IIRC we had app-compat related issues to this in 5.0 (#32107, #36936, #37720) and I'd want to make sure whatever changes we make here don't introduce new breaking changes.

[layomia]

This seems to be a breaking change of the scenario described in #51165.

A breaking change here for correctness in this edge case seems fine. The proposed changes in this PR seem safe and reasonable, but would need to come after this other PR that unifies the property visibility semantics between the source-gen and non-source gen programming models: #54526.

[ericstj]

@devsko could you rebase this, @layomia do you have any feedback for @devsko that he could address during that process?

[layomia]

@devsko, thanks for the PR! Unfortunately, per the tracking issue #51165 (comment), I do think it's a bit late in the release cycle to introduce this breaking change. We'll ping this PR when we circle back in .NET 7.