applets/weather: Improve access to the location picker

The current settings page to configure a weather station is mostly empty space, but it still launches an external dialog to pick a new location.

We can instead, have the station picker directly in the config page, so the workflow to select a new location is much more straighforward.

Now that the picker is more prominent also polish some details:

• Add placeholder texts when there is no search in progress
• Port the placeholder to Kiriami.PlaceholderMessage component
• Make the busy indicator more responsive to user typing
• Clear the list when the search field gets empty
• Separate Location and Provider labels: it prevents long strings that overflow and force the form layout into narrow/"mobile" mode

@teams/vdg

	BEFORE	AFTER
No location selected
Picking a new location
Location selected