LocationChooser: Add a "Locate" button to locate yourself

The map centers on London by default, but for the other people living
outside it may find it hard to figure out where they are. This adds a
button that calls into QtPositioning to center the map over where you
are.

src/qml/LocationChooser.qml

@@ -36,9 +36,30 @@ Components.AbstractMaximizeComponent {
             icon.name: "snap-bounding-box-center-symbolic"
             onTriggered: mapView.map.fitViewportToMapItems([mapView.locationMapItem])
             enabled: root.location !== undefined
+        },
+        Kirigami.Action {
+            text: i18nc("@action:intoolbar Determine the device's location", "Locate")
+            icon.name: "mark-location-symbolic"
+            enabled: positionSource.valid
+            onTriggered: positionSource.update()
         }
     ]
 
+    PositionSource {
+        id: positionSource
+
+        active: false
+
+        onPositionChanged: {
+            const coord = position.coordinate;
+            mapView.gpsMapItem.latitude = coord.latitude;
+            mapView.gpsMapItem.longitude = coord.longitude;
+
+            mapView.map.addMapItem(mapView.gpsMapItem);
+            mapView.map.fitViewportToMapItems([mapView.gpsMapItem])
+        }
+    }
+
     content: MapView {
         id: mapView
         map.plugin: OsmLocationPlugin.plugin
@@ -60,6 +81,15 @@ Components.AbstractMaximizeComponent {
             author: null
         }
 
+        readonly property LocationMapItem gpsMapItem: LocationMapItem {
+            latitude: 0.0
+            longitude: 0.0
+            isLive: true
+            heading: NaN
+            asset: ""
+            author: null
+        }
+
         Connections {
             target: mapView.map
             function onCopyrightLinkActivated(link: string) {