test(lsp): fix fake LSP server timeout not working (#37970)

Problem:  Fake LSP server does not timeout or respond to SIGTERM as it
          does not run the event loop.
Solution: Instead of io.read(), use stdioopen()'s on_stdin callback to
          accumulate input and use vim.wait() to wait for input.

Also, in the test suite, don't stop a session when it's not running, as
calling uv.stop() outside uv.run() will instead cause the next uv.run()
to stop immediately, which cancels the next RPC request.

0 files changed, 0 insertions, 0 deletions