feat: [AiPlatform] add Route to GroundingChunk.Maps in Vertex AI v1 (#9370)

* feat: add Route to GroundingChunk.Maps in Vertex AI v1

Adds GroundingChunk.Maps.Route (with distance_meters, duration,
encoded_polyline) and the OUTPUT_ONLY GroundingChunk.Maps.route field to
the v1 API. This surfaces route information from Google Maps grounding
responses in the public SDK.

docs: expand GroundingChunk.Maps documentation to describe route support
PiperOrigin-RevId: 950985583

Source-Link: googleapis/googleapis@fb6e47a

Source-Link: googleapis/googleapis-gen@3737ba5
Copy-Tag: eyJwIjoiQWlQbGF0Zm9ybS8uT3dsQm90LnlhbWwiLCJoIjoiMzczN2JhNTRjNzgzMjY0Y2Q1ODA0N2I0NTIxYzczNmVlMmI0ZGRhYyJ9

* 🦉 Updates from OwlBot post-processor

See https://github.com/googleapis/repo-automation-bots/blob/main/packages/owl-bot/README.md

---------

Co-authored-by: Owl Bot <gcf-owl-bot[bot]@users.noreply.github.com>

Author: gcf-owl-bot[bot]