New vscode feature, Fetch (Prune) & Delete

[devjiwonchoi]

Since there were some issues about how to delete pruned local branches at once, my initial work was migrating the OS-specific commands to vscode. I found this not the best way to handle this, so I stuck with using the git commands only.

Fetch (Prune) & Delete basically runs the following git commands:

1. git fetch --prune
2. Get the list of deleted branches internally
3. git branch -d <branch>
4. If cannot be deleted due to not being fully merged, ask the user to delete it or not
5. git branch -D <branch>

This is opened at #183955, please check it out and approve it if you like this feature.