This PR adds a built-in adapter for the basedpyright language server.
For now, it's behind the `basedpyright` feature flag, and needs to be
requested explicitly like this for staff:
```
"languages": {
"Python": {
"language_servers": ["basedpyright", "!pylsp", "!pyright"]
}
}
```
(After uninstalling the basedpyright extension.)
Release Notes:
- N/A