Android: Make the device watcher process terminate on shutdown

Terminate on IPlugin::aboutToShutdown instead of
QCoreApplication::aboutToQuit. If needed synchronously.

Added "ADB device watcher started" logging.

Fixes: QTCREATORBUG-27118
Change-Id: I483659b018c74d179b64a5a4f17cc2c27c9598a8
Reviewed-by: <github-actions-qt-creator@cristianadam.eu>
Reviewed-by: Jarek Kobus <jaroslaw.kobus@qt.io>

src/plugins/android/androidplugin.h

@@ -44,6 +44,9 @@ class AndroidPlugin final : public ExtensionSystem::IPlugin
 
     class AndroidPluginPrivate *d = nullptr;
 
+public:
+    ShutdownFlag aboutToShutdown() final;
+
 #ifdef WITH_TESTS
 private slots:
    void testAndroidSdkManagerProgressParser_data();