Nominatim lookup does not work with whole addresses

Problem/Motivation

The Nominatim API now seems very bad at doing whole address lookups, and most of the time returns no results:

e.g. https://nominatim.openstreetmap.org/ui/search.html?q=3+Arrow+Close%2C+Le...

(this is a valid address, leaving just the postcode fixes the issue)

They do now provide an API to do a structured query, which would be more suited to this use case:

https://nominatim.org/release-docs/latest/api/Search/#structured-query

e.g. https://nominatim.openstreetmap.org/ui/search.html?street=3+Arrow+Close&...

Steps to reproduce

1. Set up a Geolocation field linked to an Address field.
2. Attempt to Geocode a whole address

Proposed resolution

Create a new geocodeStructured method in GeocoderInterface to allow a structured lookup.

Remaining tasks

• Implement method
• Add tests