Is it possible to integrate Navigator into other apps as file picker?

Multiple apps use gallery-like file picker and Android provides these apps with top resources and top locations to choose from. If it's possible to use Navigator instead it could improve UX of those apps significantly. E.g. I have a lot of different folders and this gallery-like file picker in apps is always suggesting something irrelevant.

1. Is it difficult to run Navigator in embedded mode?
2. Where does Android take the gallery for embedding into filepickers?
3. Is there API for apps which behave "like a gallery" and are capable of returning file location?
4. Is it possible to make apps on a particular phone use Navigator instead of default filepicker?

Start by researching Android's embedded file-picker and gallery-provider APIs, then compare them with Navigator's current entry points. Done would require a documented, feasible integration path addressing embedded mode, file-location return APIs, and whether Navigator can be selected as the default picker.

Written by the indexing model from the issue text.