[WPAndroid] Wire up media handling with GutenbergEditorFragment and GutenbergEditPostActivity

[mzorz]

Comes from wordpress-mobile/WordPress-Android#8874

As part of the work being done inhttps://github.com/wordpress-mobile/WordPress-Android/pull/8874 to introduce a dedicated GutenbergEditPostActivity , and when after the merge and introduction of media uploads in wordpress-mobile/WordPress-Android#8879, #458 and WordPress/gutenberg#13128 happens, we'll need to rewire great part of the code to handle fail, async progress reattachment, and PostModel media relationships cleanup on opening / closing of the editor.

Tracking the tasks here

Media - related ToDo

• adapt purgeMediaToPostAssociationsIfNotInPostAnymore to work on Gutenberg contents.
• re-wire media upload reattach/progress/failed/purge/delete mechanisms once media upload is in place in Gutenberg

I'll add more tasks to this list when the time comes to tackle this one. In the meantime, all code that has been assessed as needed (even potentially) to re-wire was commented out and annotated with a // TODO for further checking in from wordpress-mobile/WordPress-Android#8874

[mzorz]

Closing this, not valid anymore as per wordpress-mobile/WordPress-Android#8874 (comment)