GH-5018: Support Gemini Grounding with Google Maps

[yasu89]

Closes #5018

Added Google Maps tool support and grounding metadata.

https://ai.google.dev/gemini-api/docs/maps-grounding

• Added Google Maps/tool widget/latitude-longitude options to GoogleGenAiChatOptions and wire them into request building via ToolConfig/RetrievalConfig, including default/runtime merging.
• Populate ChatGenerationMetadata with returned groundingMetadata for downstream access.
• Extended integration tests for Google Maps tool usage (with/without widget, with coordinates) validating grounding info presence.
• Documented new properties for enabling Google Maps grounding and widget/coordinate options.