chore: adapt lsp request handler for nvim >= 0.5.1

https://github.com/neovim/neovim/pull/15504

lua/symbols-outline/utils/lsp_utils.lua

@@ -2,6 +2,31 @@ local vim = vim
 
 local M = {}
 
+-- callback args changed in Neovim 0.5.1/0.6. See:
+-- https://github.com/neovim/neovim/pull/15504
+local function mk_handler(fn)
+  return function(...)
+    local config_or_client_id = select(4, ...)
+    local is_new = type(config_or_client_id) ~= "number"
+    if is_new then
+      fn(...)
+    else
+      local err = select(1, ...)
+      local method = select(2, ...)
+      local result = select(3, ...)
+      local client_id = select(4, ...)
+      local bufnr = select(5, ...)
+      local config = select(6, ...)
+      fn(err, result, { method = method, client_id = client_id, bufnr = bufnr }, config)
+    end
+  end
+end
+
+-- from mfussenegger/nvim-lsp-compl@29a81f3
+function M.request(bufnr, method, params, handler)
+  return vim.lsp.buf_request(bufnr, method, params, mk_handler(handler))
+end
+
 function M.is_buf_attached_to_lsp(bufnr)
     local clients = vim.lsp.buf_get_clients(bufnr or 0)
     return clients ~= nil and #clients > 0