LS doesn't shutdown properly

[raleigh-g-thompson]

At times the LS doesn't shutdown when the VSCode extension process ends.

The LS is designed to be a child process to the VSCode extension process and is expected to stop when the extension process stops.

Modify the LS to properly handle all conditions that can happen when the extension stops.

This is related to an extension issue, cqframework/vscode-cql#95