Flutter plugin for Android Studio release 71.2

First, the embedded DevTools was not functioning. That affected everyone that tried to use it.

The second problem only occurred with IntelliJ 2022.3, the latest stable release. Due to new behavior in the UI framework (*) the Flutter device selector was continuously flashing in non-Flutter projects. We can't do anything about the framework code, so we changed the device selector to be always visible, but empty.

* https://youtrack.jetbrains.com/issue/IDEA-308897/IntelliJ-2022.3-causes-custom-toolbar-widget-to-flash