Split PluginManagerInterface into PluginFactoryInterface and PluginDiscoveryInterface, as in D8.
Rename PluginFactoryInterface->getInstance to createInstance(), as in D8
PluginFactoryInterface->createInstance() should return a PluginInterface object, but not necessarily a ConfigurablePluginInterface object.
Move ViewModeFieldDisplayFormContext to a different namespace.
Remove unused class FieldInstanceDisplay