fix(LspStop): correctly stop servers and notify user #3378

## Problem
The current `LspStop` behavior is confusing and wrong:

**Server name:**
- If the server with the given `server_name` is **not attached**:
  - No notification is shown, and **all** LSP servers are stopped.
- If the server with the given `server_name` is **attached**:
  - **Incorrectly** closes all LSP servers.
- If no servers are attached:
  - `server_name` is notified as missing.

**Server ID:**
- If the server with the given `server_id` is **not attached**:
  - Uses `get_managed_clients()` function https://github.com/neovim/nvim-lspconfig/blob/541f3a2781de481bb84883889e4d9f0904250a56/plugin/lspconfig.lua#L45-L47 Which doesn't return all servers (e.g., `null-ls`), so it doesn't close all LSP clients.
- If the server with the given `server_id` is **attached**:
  - The correct LSP server is stopped (including `null-ls`).

**No arguments:**
- If servers are **attached**:
  - Stops all servers.
- If no servers are attached:
  - **Incorrectly** notifies the user with: `config "" not found`.

## Solution

**Server name:**
- If the server with the given `server_name` is **not attached**:
  - Notify the user, but **do not close** any servers.
- If the server with the given `server_name` is **attached**:
  - Close the specified server.

**Server ID:**
- If the server with the given `server_id` is **not attached**:
  - Notify the user, but **do not close** any servers.
- If the server with the given `server_id` is **attached**:
  - Close the specified server.

**No arguments:**
- If servers are **attached**:
  - Stops all servers.
- If no servers are attached:
  - No-op.

plugin/lspconfig.lua

@@ -110,36 +110,47 @@ end, {
 
 api.nvim_create_user_command('LspStop', function(info)
   local current_buf = vim.api.nvim_get_current_buf()
-  local server_id, force, server_name
+  local server_id, force, server_name, err_msg
   local arguments = vim.split(info.args, '%s')
+
+  local filter = function()
+    return true
+  end
+  local found = true
+
   for _, v in pairs(arguments) do
     if v == '++force' then
       force = true
     elseif v:find '^[0-9]+$' then
-      server_id = v
-    else
+      server_id = tonumber(v)
+      ---@param client vim.lsp.Client
+      filter = function(client)
+        return server_id == client.id
+      end
+      found = false
+      err_msg = ('nvim-lspconfig: client id "%s" not found'):format(server_id)
+    elseif v ~= '' then
       server_name = v
-    end
-  end
-
-  if not server_id then
-    local servers_on_buffer = require('lspconfig.util').get_lsp_clients { bufnr = current_buf }
-    local found = false
-    for _, client in ipairs(servers_on_buffer) do
-      if client.attached_buffers[current_buf] and (server_name and (server_name == client.config.name) or true) then
-        client.stop(force)
-        found = true
+      ---@param client vim.lsp.Client
+      filter = function(client)
+        return server_name == client.config.name
       end
+      err_msg = ('nvim-lspconfig: config "%s" not found'):format(server_name)
+      found = false
     end
+  end
 
-    if server_name and not found then
-      vim.notify(('nvim-lspconfig: config "%s" not found'):format(server_name), vim.log.levels.WARN)
-    end
-  else
-    for _, client in ipairs(get_clients_from_cmd_args(server_id)) do
+  local servers_on_buffer = require('lspconfig.util').get_lsp_clients { bufnr = current_buf }
+  for _, client in ipairs(servers_on_buffer) do
+    if client.attached_buffers[current_buf] and filter(client) then
       client.stop(force)
+      found = true
     end
   end
+
+  if not found then
+    vim.notify(err_msg, vim.log.levels.WARN)
+  end
 end, {
   desc = 'Manually stops the given language client(s)',
   nargs = '?',