LanguageClient.sendNotification fails due to change in state due to stopping client.

We are working on an LS for Odoo, and we have encountered an error that happens due to change in state.

Let me describe the scenario:

• We have a listener on onDidChangeConfiguration that based on some condition closes the client with await client.stop(15000).
• In the Client base code you also have a listener to sendNotification with the didChangeConfiguration Notification to be sent to the server.
• Since we stop the client the state is updated, but it is updated after the check you have at the top of the function Here: https://github.com/microsoft/vscode-languageserver-node/blob/d810d51297c667bd3a3f46912eb849055beb8b6b/client/src/common/client.ts#L984-L987
• At that point the state is still running, so it goes forward until it calls $start here: https://github.com/microsoft/vscode-languageserver-node/blob/d810d51297c667bd3a3f46912eb849055beb8b6b/client/src/common/client.ts#L999-L1000
• Then while it awaits this.start() which is probably already a resolved promise, the code is interrupted, and the stop function is called, so the state changes to stopping.
  https://github.com/microsoft/vscode-languageserver-node/blob/d810d51297c667bd3a3f46912eb849055beb8b6b/client/src/common/client.ts#L1755-L1765
• Then of course when it goes to this.activeConnection() it returns undefined, which then throws an error.
  https://github.com/microsoft/vscode-languageserver-node/blob/d810d51297c667bd3a3f46912eb849055beb8b6b/client/src/common/client.ts#L1232-L1234
• However in this case from our POV, it is not an error, because it was trying to send a notification while the server is stopping, and the state was stopping/stopped. I think maybe there should be a guard to check the state before raising the error so that the state is up to date.

Start in client/src/common/client.ts at sendNotification, $start, start(), and activeConnection(), following the state transitions during concurrent notification and stop calls. Reproduce the Odoo language-server scenario and inspect existing client tests, if present; done means stopping or stopped clients no longer raise this notification error while normal sends still work.