chore: Add Clirr exemptions for Protobuf 4.27.4+ runtime

[rahul2393]

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Fixes #<issue_number_goes_here> ☕️

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[gemini-code-assist]

Summary of Changes

Hello @rahul2393, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces necessary Clirr exemptions across several Google Cloud Spanner proto modules. These changes are crucial for maintaining API compatibility checks following an upgrade to Protobuf 4.27.4+ runtime. By ignoring specific structural and signature changes in the generated Protobuf code, the project can seamlessly integrate the newer Protobuf version without triggering false positives in the API compatibility reports, ensuring a smooth transition and continued stability.

Highlights

• Clirr Exemptions for Protobuf 4.27.4+ Runtime: Added a comprehensive set of Clirr exemptions to accommodate changes introduced by the Protobuf 4.27.4+ runtime upgrade. These exemptions prevent API compatibility checks from failing due to expected changes in generated code.
• Superclass Hierarchy Changes (5001): Exemptions were added for Clirr difference type 5001, which addresses the removal of GeneratedMessage and GeneratedMessage$Builder from the superclass hierarchy of generated Protobuf classes.
• Method Signature Changes (7005, 7006, 7014): New exemptions cover parameter type changes for newBuilderForType(*) (7005), return type changes for internalGetFieldAccessorTable() (7006), and instances where the getDescriptor() method was made final (7014).
• Affected Modules: These Clirr exemptions have been applied to the clirr-ignored-differences.xml files within the proto-google-cloud-spanner-admin-database-v1, proto-google-cloud-spanner-admin-instance-v1, proto-google-cloud-spanner-executor-v1, and proto-google-cloud-spanner-v1 modules.

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[gemini-code-assist]

Code Review

This pull request adds Clirr exemptions to handle binary incompatibilities introduced by upgrading to Protobuf 4.27.4+. The changes are applied consistently across four modules. I've suggested a simplification for the exemptions of difference type 5001 to improve maintainability by using a broader wildcard pattern, which is already in use for other exemptions in the same files. This would make the configuration more concise and easier to manage.

[gemini-code-assist]

The exemptions for difference type 5001 can be significantly simplified. The current patterns for different nesting levels of protobuf messages and builders are verbose and could be hard to maintain. Since the ** wildcard is already used for other difference types in this file, it can be used here to cover all classes within the package, including nested ones. This will make the configuration more concise and easier to manage across the different modules.

The same simplification can be applied to the other clirr-ignored-differences.xml files in this PR.

Suggested change

	<difference>
	<differenceType>5001</differenceType>
	<className>com/google/spanner/admin/database/v1/*</className>
	<to>com/google/protobuf/GeneratedMessage</to>
	</difference>
	<difference>
	<differenceType>5001</differenceType>
	<className>com/google/spanner/admin/database/v1/*$Builder</className>
	<to>com/google/protobuf/GeneratedMessage$Builder</to>
	</difference>
	<difference>
	<differenceType>5001</differenceType>
	<className>com/google/spanner/admin/database/v1/*$*</className>
	<to>com/google/protobuf/GeneratedMessage</to>
	</difference>
	<difference>
	<differenceType>5001</differenceType>
	<className>com/google/spanner/admin/database/v1/*$*$Builder</className>
	<to>com/google/protobuf/GeneratedMessage$Builder</to>
	</difference>
	<difference>
	<differenceType>5001</differenceType>
	<className>com/google/spanner/admin/database/v1/*$*$*</className>
	<to>com/google/protobuf/GeneratedMessage</to>
	</difference>
	<difference>
	<differenceType>5001</differenceType>
	<className>com/google/spanner/admin/database/v1/*$*$*$Builder</className>
	<to>com/google/protobuf/GeneratedMessage$Builder</to>
	</difference>
	<difference>
	<differenceType>5001</differenceType>
	<className>com/google/spanner/admin/database/v1/*Proto</className>
	<to>com/google/protobuf/GeneratedFile</to>
	</difference>
	<difference>
	<differenceType>5001</differenceType>
	<className>com/google/spanner/admin/database/v1/**</className>
	<to>com/google/protobuf/GeneratedMessage</to>
	</difference>
	<difference>
	<differenceType>5001</differenceType>
	<className>com/google/spanner/admin/database/v1/**</className>
	<to>com/google/protobuf/GeneratedMessage$Builder</to>
	</difference>
	<difference>
	<differenceType>5001</differenceType>
	<className>com/google/spanner/admin/database/v1/*Proto</className>
	<to>com/google/protobuf/GeneratedFile</to>
	</difference>