static function for popdown

### Problem

We have a signal `public signal void close ();` in Indicator but often we want to call popdown from other classes than the main indicator class. We can do that either by chaining up signals—which is kinda gross—or ignoring this function altogether and using `get_ancestor`. Neither of which are super ideal

### Proposal

A function we can call from any part of the indicator to close the popover

### Prior Art (Optional)

_No response_