With this we should be able to handle `setState()`s that try to resize
the currently open editor. This could pop up when using the preset
browser in REAPER with plugins that recall their old size when loading a
preset.
By directly stopping the IO context there was a chance that a task would
get cancelled outright if all stars aligned in the wrong way. Stopping
the IO context could happen between posting the task to the context and
waiting for it. This approach is much safer as we cannot drop any work
this way.
This would cause crashes in Bitwig, as `RunLoopTasks`' destructor would
not be run after the event handler has been unregistered, and we
unregister the event handler in that destructor.
I've never seen this happen, but now this too would support deeply
nested mutual recursion just like we implemented in
`Vst3PlugViewProxyImpl`. Better safe than sorry.
This was a bit of a tricky one because it requires simulating mutual
recursion, but it's needed for REAPER as otherwide calls to
`IPlugFrame::resizeView()` and `IContextMenu::popup()` might cause
REAPER to segfault because its GUI is not thread safe.
Robbert van der Helm