Manually reorder subscriptions lists

[ghost]

Checklist

• I made sure that there are no existing issues - open or closed - which I could contribute my information to.
• I'm aware that this is a request for NewPipe itself and that requests for adding a new service need to be made at NewPipeExtractor.
• I have taken the time to fill in all the required details. I understand that the feature request will be dismissed otherwise.
• This issue contains only one feature request.
• I have read and understood the contribution guidelines.

Feature description

Add two-bar handle to move subscriptions up and down. Just like #8221 did for playlists, but for subscriptions.

Why do you want this feature?

I would like to sort subscriptions some down others up for convenience.

[GGAutomaton]

I would like to work on this issue.

[GGAutomaton]

Current progress:

• Add a new column display_index in the database.
• Implement an algorithm to merge local playlists and remote playlists by index. If they have the same index, sort them by name.
• If the saved index doesn't match the actual display index for some reason (e.g., setting to all zero after database migration, or the index is not continuous after deletion), save the new index to the database.
• A newly added playlist is always on the top of the bookmark.
• UI design. Add item handle.
• Debounced saver.

[nerdguy1338]

Current progress:

• Add a new column display_index in the database.
• Implement an algorithm to merge local playlists and remote playlists by index. If they have the same index, sort them by name.
• If the saved index doesn't match the actual display index for some reason (e.g., setting to all zero after database migration, or the index is not continuous after deletion), save the new index to the database.
• A newly added playlist is always on the top of the bookmark.
• UI design. Add item handle.
• Debounced saver.

Speaking of merging playlists, could that be an option please? Merge multiple playlists into one big one, optionally remove duplicate videos?