[2.0.0-alpha1] ui_icon_autocomplete must send storable config

There is a chance UnsupportedDataTypeConfigException is because you are missing a schema.yml file for the type and not really a storage problem.

Still, I agree you should store only icon id and settings.

But with the current approach it's cleaner to send the object around, advantages are:

• avoid some dependency injection
• allow quick interface test instanceof IconDefinitionInterface instead of loading
• with only full id (iconset_id:icon_id) we introduce multiple explode() for the same thing instead of getIconsetId() or getId(), meaning if we change the separator or the id it needs to be changed everywhere
• same for getRenderable(), we need to load the icon before when it's not needed with the object

Because the FormElement is meant to be generic, the rule is to match most implementations, but not all at all cost if it means more code on all other implementations.

Even more the autocomplete is just one implementation for a picker and should be split in the future to allow other type of selectors.

Need to check if a simple solution can be found for ui patterns and if not first a property is a mitigating approach before adding code in all other implementations.

Because this is now in core, we can close.