Investigate & implement alternative trip address autocomplete libraries

We migrated the same API used for address autocomplete from the old version of the frontend, Mapbox Address Autocomplete API, which is reliant on Conveyal's Mapbox account and API Key. This API isn't as performant as we'd like and presents risk since we don't manage the account, so we should investigate our options.
1. Look into address autocomplete libraries we can use in place of mapbox
- Ideally can constraint addresses by polygon or bbox
2. If address autocomplete available but responses do not include lat/lng values, also add forward geocoding (ex: [Esri](https://www.esri.com/en-us/arcgis/products/arcgis-world-geocoder)'s forward geocoding API)

If implementing new library seems feasible, accomplish within this card. If we need to continue with Mapbox, ask if BHA can create account and new API key.

The issue names no files, tests, or entry points. Start by locating the current Mapbox Address Autocomplete integration in the TypeScript frontend, then evaluate alternatives against polygon or bounding-box constraints and lat/lng availability; done means implementing a feasible replacement or documenting the decision to retain Mapbox and request a BHA account and API key.

Written by the indexing model from the issue text.