Track down all manual calls to dispose() in the IntelliJ Plugin

Some classes like `FlutterWidgetPerf`
implement the Disposable interface but have `dispose()`
called manually which is counter to how `dispose()` should be called for a properly functioning IntelliJ plugin.

Mixing manual and automatic calls to dispose leads to confusing bugs like
https://github.com/flutter/flutter-intellij/issues/6042