vcs_menu: Streamline branch creation from branch selector (#18712)

This PR streamlines the branch creation from the branch selector when
searching for a branch that does not exist.

The branch selector will show the available branches, as it does today:

<img width="576" alt="Screenshot 2024-10-03 at 4 01 25 PM"
src="https://github.com/user-attachments/assets/e1904f5b-4aad-4f88-901d-ab9422ec18bb">

When entering the name of a branch that does not exist, the picker will
be populated with an entry to create a new branch:

<img width="570" alt="Screenshot 2024-10-03 at 4 01 37 PM"
src="https://github.com/user-attachments/assets/07f8d12c-9422-4fd8-a6dc-ae450e297a13">

Selecting that entry will create the branch and switch to it.

Release Notes:

- Streamlined creating a new branch from the branch selector.