Filesystem Explorer: Add a minimum width and height

This prevents to reduce the window to a minimum of 1px (default), where
it gets hard to expand the window again. As a drive-by improve the
visualization of highlighted files.

Fixes: QTBUG-119785
Change-Id: Ib4a7f37fa4886589bad4cce534a9d73c352dd4ee
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
(cherry picked from commit eaaa8647da)

examples/quickcontrols/filesystemexplorer/Main.qml

@@ -16,6 +16,8 @@ ApplicationWindow {
 
     width: 1100
     height: 600
+    minimumWidth: 200
+    minimumHeight: 100
     visible: true
     color: Colors.background
     flags: Qt.Window | Qt.FramelessWindowHint

examples/quickcontrols/filesystemexplorer/qml/FileSystemView.qml

@@ -78,11 +78,20 @@ Rectangle {
 
                 anchors.fill: directoryIcon
                 source: directoryIcon
-
-                colorizationColor: (treeDelegate.expanded && treeDelegate.hasChildren)
-                                         ? Colors.color2 : Colors.folder
                 colorization: 1.0
                 brightness: 1.0
+                colorizationColor: {
+                    const isFile = treeDelegate.index === fileSystemTreeView.lastIndex
+                                    && !treeDelegate.hasChildren;
+                    if (isFile)
+                        return Qt.lighter(Colors.folder, 3)
+
+                    const isExpandedFolder = treeDelegate.expanded && treeDelegate.hasChildren;
+                    if (isExpandedFolder)
+                        return Colors.color2
+                    else
+                        return Colors.folder
+                }
             }
 
             HoverHandler {