Add dependency for Qt Quick Controls 2

Summary: The app requires having Qt Quick Controls installed to launch

Test Plan:
 - Attempt to launch app without Qt Quick Controls 2 package installed
 - App should complain and not appear
 - Attempt to launch app with Qt Quick Controls 2
 - App should launch and display properly

Reviewers: #kde_connect, apol

Reviewed By: #kde_connect, apol

Subscribers: apol, kdeconnect

Tags: #kde_connect

Differential Revision: https://phabricator.kde.org/D16718

CMakeLists.txt

@@ -85,7 +85,14 @@ add_subdirectory(data)
 
 option(EXPERIMENTALAPP_ENABLED OFF)
 if(EXPERIMENTALAPP_ENABLED)
-    add_subdirectory(app)
+  find_package(KF5Kirigami2)
+  set_package_properties(KF5Kirigami2 PROPERTIES
+    DESCRIPTION "QtQuick plugins to build user interfaces based on KDE UX guidelines"
+    PURPOSE "Required for kcapp"
+    URL "https://www.kde.org/products/kirigami/"
+    TYPE RUNTIME
+)
+  add_subdirectory(app)
 endif()
 add_subdirectory(plugins)
 add_subdirectory(cli)