Co-authored-by: Eric Amodio <eamodio@users.noreply.github.com>

Closes #2252
Closes #2448
Follow-up to 5f95876a97

- Controlled by the `gitlens.graph.experimental.location` setting

- Honors `createBranch` flag for naming the worktree folder
- Falls back to the qualified remote branch name if the branch name already exists
- Always uses the qualified remote branch name via GHPR command

Fixes tags on the Graph for remote repos

Uses the core git fetch command instead of a command-line
git fetch so VsCode will prompt the user for their username
and password. Pull & push also use their corresponding core commands.

Aligns worktree open prompting using quick picks