feat(pack): add built-in plugin manager vim.pack

Problem: No built-in plugin manager

Solution: Add built-in plugin manager

Co-authored-by: Lewis Russell <lewis6991@gmail.com>

runtime/lua/vim/_editor.lua

@@ -39,6 +39,7 @@ for k, v in pairs({
   health = true,
   secure = true,
   snippet = true,
+  pack = true,
   _watch = true,
 }) do
   vim._submodules[k] = v