Allow mouse events when transient scroll bars are hidden

On mac, while transient scroll bars are not visible it was not
possible to interact with the viewport as the mouse events were
consumed by the scroll view.

This makes the ScrollBar mouse area disabled before a scroll is
triggered. Note that I also added a minor workaround to ensure
that we update the mouse cursor.

Task-number: QTBUG-32400
Change-Id: If091edf054fcab65feb9b8c8e5c45e25431f4be4
Reviewed-by: Gabriel de Dietrich <gabriel.dedietrich@digia.com>

src/private/ScrollBar.qml

@@ -50,6 +50,8 @@ import QtQuick.Controls.Private 1.0
 Item {
     id: scrollbar
 
+    property bool isTransient: false
+    property bool active: false
     property int orientation: Qt.Horizontal
     property alias minimumValue: slider.minimumValue
     property alias maximumValue: slider.maximumValue
@@ -85,13 +87,12 @@ Item {
 
     MouseArea {
         id: internal
-
         property bool horizontal: orientation === Qt.Horizontal
         property int pageStep: internal.horizontal ? width : height
         property int singleStep: 20
         property bool scrollToClickposition: internal.scrollToClickPosition
-
         anchors.fill: parent
+        cursorShape: __panel.visible ? Qt.ArrowCursor : Qt.IBeamCursor // forces a cursor change
 
         property bool autoincrement: false
         property bool scrollToClickPosition: __style ? __style.scrollToClickedPosition : 0

src/private/ScrollViewHelper.qml

@@ -121,8 +121,9 @@ Item {
 
     ScrollBar {
         id: hscrollbar
-        property bool isTransient: !!__panel && !!__panel.transient
-        property bool active: !!__panel && (__panel.sunken || __panel.activeControl != "none")
+        isTransient: !!__panel && !!__panel.transient
+        active: !!__panel && (__panel.sunken || __panel.activeControl !== "none")
+        enabled: !isTransient || __panel.visible
         orientation: Qt.Horizontal
         visible: contentWidth > availableWidth
         height: visible ? implicitHeight : 0
@@ -161,8 +162,9 @@ Item {
 
     ScrollBar {
         id: vscrollbar
-        property bool isTransient: !!__panel && !!__panel.transient
-        property bool active: !!__panel && (__panel.sunken || __panel.activeControl !== "none")
+        isTransient: !!__panel && !!__panel.transient
+        active: !!__panel && (__panel.sunken || __panel.activeControl !== "none")
+        enabled: !isTransient || __panel.visible
         orientation: Qt.Vertical
         visible: contentHeight > availableHeight
         width: visible ? implicitWidth : 0