Currently, we're using ad-hoc solution to report progress to vscode extension, using telemetry events. This requires specific client-side support. There's now a better option: reporting the progress using $/progress notifications, that are allowed during the initialize phase if client sends workDoneToken in initialize request. Using it would allow reporting the progress to any compliant client, not just our vscode ext.

Spec links:

• initialize request
• workdone notifications

Open questions:

1. How do we prevent duplicate reports when older vscode ext connects to newer psalm server? Client sniffing?
2. Neovim doesn't seem to be sending workDoneToken in initialize requests (this can probably be overridden somewhere).