StandardDropdown: Add Flickable and ScrollBar to droplist

This commit adds a Flickable and ScrollBar to the
StandardDropdown component. The use case is for the list
of fiat currencies which is flowing off-screen. Tested on
ASUSTek laptop touchpad.

Fixes: 302490e ("Add additional fiat currencies")

components/StandardDropdown.qml

@@ -146,11 +146,37 @@ ColumnLayout {
         padding: 0
         closePolicy: Popup.CloseOnEscape | Popup.CloseOnPressOutsideParent
 
+        Flickable {
+            id: flickable
+            flickableDirection: Flickable.VerticalFlick 
+            clip: true
+            boundsBehavior: Flickable.StopAtBounds
+            contentHeight: contentItem.childrenRect.height
+            contentWidth: contentItem.childrenRect.width
+            width: dropdown.width
+            height: 240
+            y: head.height + head.y
+            flickDeceleration: 35000
+            onAtYEndChanged: {
+                if (flickable.atYEnd) {
+                    // hack for getting that last item Flickable seems to hate showing
+                }
+            }
+            // put a mouse area on the flickable since we don't have access to the previous one
+            MouseArea {
+                id: dropArea2
+                anchors.fill: parent
+                onClicked: dropdown.expanded ? popup.close() : popup.open()
+                hoverEnabled: true
+                cursorShape: Qt.ArrowCursor
+                onPressed: flickable.interactive = false
+                onReleased: flickable.interactive = true
+            }
+            ScrollBar.vertical: ScrollBar {}
             Rectangle {
                 id: droplist
                 anchors.left: parent.left
                 width: dropdown.width
-            y: head.y + head.height
                 clip: true
                 height: dropdown.expanded ? columnid.height : 0
                 color: dropdown.pressedColor
@@ -226,3 +252,4 @@ ColumnLayout {
             }
         }
     }
+}