Document provider enhancement

[tobiasKaminsky]

This is somekind of a meta issue:

Issues regarding document provider:

• Can't edit text files with external app #2952
• Support Intent.ACTION_OPEN_DOCUMENT_TREE #303
• Implementation of the StorageProvider interface #2258
• Editing files from nextcloud app #3422
• Thumbnails don't show when NC used as a document provider #1827

Google sample project: https://github.com/googlesamples/android-StorageProvider
Info: https://developer.android.com/guide/topics/providers/create-document-provider

PR fixing it:

• Documents Provider: Base for updated documents provider #3432
• Documents Provider: allow editing of files, saves back to server #3433
• Document Provider: new folder #3434
• Document provider: delete file #3435
• Document provider: allow rename #3436
• Document provider: allow copy/move of file/folder #3454 (was Document provider: copy move #3437)
• Document provider: refresh  #3455 (was Document provider: refresh #3438)
• Document provider: new file #3439
• Document provider: show thumbnail, if available, else fetch from server #3453 (was Document provider: support for remote thumbnails #3442)

So once all PRs are tested, we should ping the issues and get a verification that they are solved.

[AndyScherzinger]

🎉 awesome work @tobiasKaminsky - also sub-tasks have been merged and are done. Do you ping the issues related to this one (as mentione ddin the issues description?).

Should we close this issue (since DONE) or do you want to keep it open depending on the issues feedbacks?

[tobiasKaminsky]

I'll close this and ping the others.