Component::onDependencyRemoval() should be an uninstall validator

Overview

Component::onDependencyRemoval() replaces the current component version with a fallback plugin.

However if this code is running, it would usually mean that a module or theme is being uninstalled.

Replacing the component (e.g. if it's an SDC) with a fallback plugin silently could mean breaking a lot of content - on the basis that the user might know where that SDC comes from.

So... I think this could be an uninstall validator.

Proposed resolution

User interface changes