Feature: Allow deleting of local Git branches

[ferrariofilippo]

Resolved / Related Issues

• Were these changes approved in an issue or discussion with the project maintainers? In order to prevent extra work, feature requests and changes to the codebase must be approved before the pull request will be reviewed. This prevents extra work for the contributors and maintainers.
  Closes Feature: Allow deleting of local Git branches #13592

Important

• Backup your repo before testing this feature
• Check this PR doesn't affect performance in Git folders
  • I had to revert a change made in Code quality: Move Git operations to a different thread #13608 because Ahead / Behind wouldn't be update after Pulls (see BaseShellPage.cs)

Validation
How did you test these changes?

• Did you build the app and test your changes?
• Did you check for accessibility? You can use Accessibility Insights for this.
• Did you remove any strings from the en-us resource file?
  • Did you search the solution to see if the string is still being used?
• Did you implement any design changes to an existing feature?
  • Was this change approved?
• Are there any other steps that were used to validate these changes?
  1. Open a git repo
  2. Click on the branch name in the status bar
  3. Click on Delete to delete a local branch
  4. Click on Cancel and make sure the branch is still there
  5. Repeat but click on Continue and check that the branch is deleted

Screenshots (optional)

[yaira2]

We still haven't finalized the design for this feature. I'll try to finish this up over the next few days.