[Bitbucket] Handle draft pull requests

**Is your feature request related to a problem? Please describe.**
Now that Bitbucket Cloud has draft pull requests, I can not filter those out or discern which are drafts from the VS Code addon.

**Describe the solution you'd like**
- The ability to see clearly on a pull request that it is a draft would be a great start to understand what the state of the PR is when I'm looking at it.
- The "Showing pull requests to review" filter should probably exclude draft pull requests.
- Adding a separate filter to show only draft pull requests may be helpful too.

The issue names no files, tests, or entry points. Trace how Bitbucket pull requests are represented in the VS Code addon, where review filters are applied, and where pull request state is rendered. Done means draft status is discernible and the review filter excludes drafts, with any separate draft filter behavior defined and tested.

Written by the indexing model from the issue text.