[1.0.0-beta2] Plugins must add dependencies to config entities

Problem/Motivation

We need to add the dependency to the module or theme providing the icon pach:

• when an icon to a entity view display config entity using a field formatter
• when configuring allowed_icon_pack in a entity form display config entity using a field widget
• when configuring allowed_icon_pack in a editor config entity using a Ckeditor5 plugin
• ... what else?

So, Drupal will now what to do (warn, update the config...) when we disable the module or the theme.

Config dependency ? If we disable a module or theme which is providign an iconpack >> create issue but maybe being silent is enough

Proposed resolution

Maybe we can consider the silent fallback we have today is enough. Or we can also add some dependency management.

Do we need to implement DependentPluginInterface::calculateDependencies?