[Feature] Limit geocoder search to current viewport

**Is your feature request related to a problem? Please describe.**
As a user sometimes I want the search results in geocoder dropdown to be limited to the area that I'm viewing. Having this option would be nice.

**Describe the solution you'd like**
Add additional trigger control to Geocoder config panel. Mapbox supports bbox(viewport area) limits for Geocoder.

**Describe alternatives you've considered**
Making viewport search limit as a default one

**Additional context**
Here's simple design mockup: