fix(lsp): close timer when client exits (#36795)

Also, don't start the timer at all when a previous shutdown failed, as
in this case a forced shutdown is used and no timer is needed.

This fixes most of the delays caused by #36750.
The delays caused by #36378 still seem to remain.

runtime/lua/vim/lsp/client.lua

@@ -219,6 +219,9 @@ local all_clients = {}
 --- Whether on-type formatting is enabled for this client.
 --- @field _otf_enabled boolean?
 ---
+--- Timer for stop() with timeout.
+--- @field private _shutdown_timer uv.uv_timer_t?
+---
 --- Track this so that we can escalate automatically if we've already tried a
 --- graceful shutdown
 --- @field private _graceful_shutdown_failed true?
@@ -882,12 +885,6 @@ end
 ---
 --- @param force? boolean|integer
 function Client:stop(force)
-  if type(force) == 'number' then
-    vim.defer_fn(function()
-      self:stop(true)
-    end, force)
-  end
-
   local rpc = self.rpc
   if rpc.is_closing() then
     return
@@ -902,6 +899,13 @@ function Client:stop(force)
     return
   end
 
+  if type(force) == 'number' then
+    self._shutdown_timer = vim.defer_fn(function()
+      self._shutdown_timer = nil
+      self:stop(true)
+    end, force)
+  end
+
   -- Sending a signal after a process has exited is acceptable.
   rpc.request('shutdown', nil, function(err, _)
     if err == nil then
@@ -1309,6 +1313,11 @@ end
 --- @param code integer) exit code of the process
 --- @param signal integer the signal used to terminate (if any)
 function Client:_on_exit(code, signal)
+  if self._shutdown_timer and not self._shutdown_timer:is_closing() then
+    self._shutdown_timer:close()
+    self._shutdown_timer = nil
+  end
+
   vim.schedule(function()
     for bufnr in pairs(self.attached_buffers) do
       self:_on_detach(bufnr)