Filesystem Explorer: Guard against mobile usage

It was observed that users try to run this example on mobile platforms.
It was never designed for such a usecase and is therefore not supported.

Ref: https://camg.me/qt-mobile-2023/#filesystem

Additionally mention that this is a desktop example in the docs.

Change-Id: I55205e3f2cb3a45aaf18f2a52ea24f54ab8e39bd
Reviewed-by: Mitch Curtis <mitch.curtis@qt.io>
(cherry picked from commit 9e4f24e749)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
(cherry picked from commit 15d27caf01)

examples/quickcontrols/CMakeLists.txt

@@ -13,7 +13,7 @@ qt_internal_add_example(texteditor)
 qt_internal_add_example(contactlist)
 qt_internal_add_example(wearable)
 qt_internal_add_example(imagine/automotive)
-if (TARGET Qt6::Svg)
+if (TARGET Qt6::Svg AND NOT ANDROID AND NOT IOS)
     qt_internal_add_example(filesystemexplorer)
 endif()
 if(TARGET Qt6::Widgets)

examples/quickcontrols/filesystemexplorer/CMakeLists.txt

@@ -4,6 +4,11 @@
 cmake_minimum_required(VERSION 3.16)
 project(filesystemexplorer LANGUAGES CXX)
 
+if (ANDROID OR IOS)
+    message(FATAL_ERROR "Platform is not supported")
+    return()
+endif ()
+
 if (NOT DEFINED INSTALL_EXAMPLESDIR)
     set(INSTALL_EXAMPLESDIR "examples")
 endif ()

examples/quickcontrols/filesystemexplorer/doc/src/qtquickcontrols-filesystemexplorer.qdoc

@@ -6,8 +6,8 @@
     \meta tags {quickcontrols, layout, styling, treeview}
     \title File System Explorer
     \ingroup qtquickcontrols-examples
-    \brief A QML app utilizing customized Qt Quick Controls to display text
-    files from a filesystem.
+    \brief A desktop QML app utilizing customized Qt Quick Controls to display
+    text files from a filesystem.
 
     In this example, a modern layout is used that consists of three major
     components. There is an icon-based \e {Sidebar} to the left, followed by a

examples/quickcontrols/filesystemexplorer/filesystemexplorer.pro

@@ -1,6 +1,10 @@
 # Copyright (C) 2023 The Qt Company Ltd.
 # SPDX-License-Identifier: BSD-3-Clause
 
+android|ios {
+    error( "Platform not supported" )
+}
+
 QT += quick
 
 CONFIG += qmltypes

examples/quickcontrols/quickcontrols.pro

@@ -5,8 +5,11 @@ SUBDIRS += \
     texteditor \
     contactlist \
     wearable \
-    filesystemexplorer \
     imagine/automotive
 
+win32|macos|unix {
+    qtHaveModule(svg): SUBDIRS += filesystemexplorer
+}
+
 qtHaveModule(sql): SUBDIRS += eventcalendar
 qtHaveModule(widgets): SUBDIRS += flatstyle