Remove the member `PluginView::m_isResizable` and it's associated method `setResizable`. Turn `isResizable` into a virtual method.
The reasoning is that whether or not an effect can be resized depends on its implementation. Therefore does not make sense to have a method like `setResizable`. If the underlying implementation does not support resizing then it would not make sense to call `setResizable(true)`. So `isResizable` now describes the underlying ability of a plugin to resize. It's then up to the clients of that method to decide how to treat the result of `isResizable`, i.e. if they want to make use of the ability to resize or not.