[TS MVP] Create typings for editor config

[arkflpc]

To achieve the first goal of #11704 (Improving the DX for the community), it would be very helpful to have editor config statically typed.

The config can be used in different contexts:

1. As a parameter to Editor.create()
2. Within plugins: editor.config.define() in constructor and editor.config.get() later.

I would try to solve the first one and at least investigate if we can achieve the second.

If possible, we should avoid centralized type for the config and assemble it somehow from definitions near plugins that define them. We wouldn't introduce unnecessary coupling, and the user would be able to extend it as well. Maybe we could use some magic type interference based on plugin classes provided to create() method. If that fails, the centralized config type covering only plugins included in ckeditor5 is better than the fully dynamic one.

Part of #11708.

[arkflpc]

At least one plugin that declares its config should be rewritten first. Then, we could test in different package if this config is visible as a member of EditorConfig interface.

[arkflpc]

Seems to be done in other tickets