Implement SearchEngineProvider using MLS

[pocmo]

Also see: #1720, mozilla-mobile/fenix#3869

In Fennec we do a region lookup via MLS. Let's port this to AC so that we can use it in Fenix. Our updated list.json requires a region and using the locale for that is not that helpful.

┆Issue is synchronized with this Jira Task

[vesta0]

Spoke to Mike, let's try to fix this in this sprint please.

[pocmo]

• Code in Fennec: https://searchfox.org/mozilla-central/rev/da3f3eaaacb6fb344fd21ac29ace2da0e33f12d3/mobile/android/base/java/org/mozilla/gecko/search/SearchEngineManager.java#374-428
• https://location.services.mozilla.com/
• API docs: https://mozilla.github.io/ichnaea/api/index.html
• Seems like this is a good candidate for a new component, e.g. service-mls or service-mozillalocationservice or ... ... or maybe a generic service-location where we can place more code like Fuzzy location/region provider #1720
• Code needs to be ported to use concept-fetch
• A token is needed for the service. So we'd need to request one for Fenix and potentially Reference Browser. There's a test token for development purposes.

[pocmo]

Moving this out of the sprint. Filed #3934 which seems to be a prerequisite to finishing this.