Support Checkout Pull Request in Dev Container

[rebornix]

• Browse a PR from Copilot
• Run "Checkout PR in Dev Container" from context menu (this doesn't work now and requires fix https://github.com/microsoft/vscode-remote-containers/pull/985)
• After the PR is opened in a dev container volume, the PR view reveals automatically
• I would expect "active pull request" tool to be attached as well since this PR is Copilot generated