The patch in #13 is useful if you want to write a custom migration but it is ...

The patch in #13 is useful if you want to write a custom migration but it is not really necessary for an upgrade. As such, I am not including that process plugin in this patch, which purely handles an upgrade.

Right now, this patch depends on a core patch at #2787639-5: MigrateCckFieldPluginManager mixes up its behaviour for creating and loading definitions. With this patch, I am able to migrate the address field itself, the instance, and the widget configuration, but the formatter configuration does not get migrated due to another bug (which I will raise in the core issue queue).