pkl-vscode 0.19.0 is released

[bioball]

pkl-vscode 0.19.0 is released!

This improves syntax highlighting, and also bumps the bundled Pkl Language Server to version 0.3.0.

This also will auto-discover new 0.x versions of Pkl Language Server.

For more details, consult the release notes.

Thanks to @KushalP for their contribution!