[release/6.0] Src gen: use GetBestTypeByMetadataName instead of GetTypeByMetadataName

[steveharter]

Backport of #59092 to release/6.0

Fixes#57349

See also the related backport for System.Text.Json at #58766.

Customer Impact

If there is more than one type with the same name (namespace and class name) but in different assemblies, the conflict may cause source-generation to fail for the logging source generator. If the duplicate types are not be owned by the customer, there is no work-around without the changes in this PR.

Testing

A new test was added; System.Text.Json also has a test that uses the same GetBestTypeByMetadataName() extension method.

Risk

Low; this is a simple 1:1 method replacement which has been previously tested in System.Text.Json (which has a unit test) and by Roslyn. The guidance and extension method is provided by the Roslyn team.

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Issue Details

---

Backport of #59092 to release/6.0

Fixes #57349

See also the related backport for System.Text.Json at #58766.

Customer Impact

If there is more than one type with the same name (namespace and class name) but in different assemblies, the conflict may cause source-generation to fail for the logging source generator. If the duplicate types are not be owned by the customer, there is no work-around without the changes in this PR.

Testing

A new test was added; System.Text.Json also has a test that uses the same GetBestTypeByMetadataName() extension method.

Risk

Low; this is a simple 1:1 method replacement which has been previously tested in System.Text.Json (which has a unit test) and by Roslyn. The guidance and extension method is provided by the Roslyn team.

Author:	steveharter
Assignees:	steveharter
Labels:	Servicing-consider, area-Extensions-Logging
Milestone:	6.0.0

[danmoseley]

OK - this is extending the proven fix from Json. Please send mail if you haven't already.

[steveharter]

Servicing approved via mail.