Handle requests received after shutdown message (#16262)
## Summary
This PR should help in
https://github.com/astral-sh/ruff-vscode/issues/676.
There are two issues that this is trying to fix all related to the way
shutdown should happen as per the protocol:
1. After the server handled the [shutdown
request](https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#shutdown)
and while waiting for the exit notification:
> If a server receives requests after a shutdown request those requests
should error with `InvalidRequest`.
But, we raised an error and exited. This PR fixes it by entering a loop
which responds to any request during this period with `InvalidRequest`
2. If the server received an [exit
notification](https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#exit)
but the shutdown request was never received, the server handled that by
logging and exiting with success but as per the spec:
> The server should exit with success code 0 if the shutdown request has
been received before; otherwise with error code 1.
So, this PR fixes that as well by raising an error in this case.
## Test Plan
I'm not sure how to go about testing this without using a mock server.
