update installer with sync and some fixes

- add sync method for installing using `system`
- remove `descriptions` in command configs
- use install(lang) in ensure_installed and make it compatible

lua/nvim-treesitter/info.lua

@@ -81,16 +81,14 @@ M.commands = {
     run = install_info,
     args = {
       "-nargs=0",
-    },
-    description = '`:TSInstallInfo` print installation state for every filetype'
+    }
   },
   TSModuleInfo = {
     run = module_info,
     args = {
       "-nargs=?",
       "-complete=custom,v:lua.ts_available_modules"
-    },
-    description = '`:TSModuleInfo` print module state for every filetype, if module is specified, only for current module'
+    }
   }
 }