.Net: Fix Google Gemini API compatibility by filtering unsupported format fields

[Copilot]

Problem

Google's Gemini API has updated their validation to only accept "enum" and "date-time" format fields for string types in OpenAPI schemas. This causes function calls with GUID/UUID parameters to fail with validation errors like:

"GenerateContentRequest.tools[0].function_declarations[1].parameters.properties[myReference].properties[MyProperty].format: only 'enum' and 'date-time' are supported for STRING type"

When .NET serializes schemas for types like Guid, it includes format fields (e.g., "format": "uuid") that are now rejected by Google's API.

Solution

Modified the TransformOpenApi3Object method in GeminiRequest.cs to strip unsupported format fields from string type properties during schema transformation. The fix:

1. Preserves supported formats: "enum" and "date-time" formats are kept as required by Google's API
2. Removes unsupported formats: All other format fields (like "uuid", "email", "phone", etc.) are stripped from string properties
3. Maintains existing behavior: All other schema transformations continue to work as before

Changes

• Added format field filtering logic in TransformOpenApi3Object method
• Added comprehensive test ResponseSchemaStripsUnsupportedFormatFields to verify the behavior
• Fixed variable name conflict in the same method scope

Testing

• ✅ New test verifies that unsupported formats are stripped while supported formats are preserved
• ✅ All 317 existing Google connector unit tests continue to pass
• ✅ All 34 existing GeminiRequestTests continue to pass

This minimal change ensures compatibility with Google's updated API validation while preserving all existing functionality.

• Fixes .Net: Bug: Google Connector Fails with GUIDs in Function Calls #12957

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[rogerbarreto]

Closing for now, will re-open later.