Show a loading indicator for Views Proximity Filter Autocomplete

Problem/Motivation

The Geocoder Views Proximity Filter is currentl missing a visual hint (if autocomplete is enabled) that this is an autocomplete field. While it's fetching results, there's also no indicator so that users may press enter before the results are shown. This leads to "No results found" errors.

Steps to reproduce

Proposed resolution

Add a greyed out autocomplete indicator (ring) on the right side of the input field, if autocomplete is not active. If autocomplete is fetchig results, animate it to spin.

Think I saw this somewhere in Drupal for the Autocomplete field, but I'm not sure if it's theme-specific. What do you think?

Remaining tasks

User interface changes

API changes

Data model changes