pkg(nixvim): Add lazy-load file to use AutoCmd to load plugin

pkgs/nixvim/util/lazy-load.nix

@@ -0,0 +1,38 @@
+{...}: {
+  extraConfigLuaPre =
+    #lua
+    ''
+      do
+        _M.plugins = {}
+        _M.load = function(name)
+          _M.plugins = vim.tbl_deep_extend("force", _M.plugins, {
+            name = {
+              loaded = true,
+            },
+          })
+          vim.schedule(function()
+            vim.api.nvim_exec_autocmds("User", { pattern = "LazyLoad", modeline = false, data = name })
+          end)
+        end
+        _M._is_loaded = function(name)
+          local plugins = _M.plugins
+          return plugins[name] and plugins[name].loaded
+        end
+        _M.on_load = function(name, fn)
+          if _M._is_loaded(name) then
+            fn(name)
+          else
+            vim.api.nvim_create_autocmd("User", {
+              pattern = "LazyLoad",
+              callback = function(event)
+                if event.data == name then
+                  fn(name)
+                  return true
+                end
+              end,
+            })
+          end
+        end
+      end
+    '';
+}