feat(startup): load builtin plugins with --clean #15893

Closes #15605

runtime/doc/starting.txt

@@ -90,10 +90,11 @@ argument.
 		See |info-message| about capturing the text.
 
 							*--clean*
---clean		Equivalent to "-u NONE -i NONE":
+--clean		Mimics a fresh install of Nvim:
 		- Skips initializations from files and environment variables.
 		- No 'shada' file is read or written.
 		- Excludes user directories from 'runtimepath'
+		- Loads builtin plugins, unlike "-u NONE -i NONE".
 
 							*--noplugin*
 --noplugin	Skip loading plugins.  Resets the 'loadplugins' option.

src/nvim/main.c

@@ -345,7 +345,8 @@ int main(int argc, char **argv)
   // Reset 'loadplugins' for "-u NONE" before "--cmd" arguments.
   // Allows for setting 'loadplugins' there.
   if (params.use_vimrc != NULL && strequal(params.use_vimrc, "NONE")) {
-    p_lpl = false;
+    // When using --clean we still want to load plugins
+    p_lpl = params.clean;
   }
 
   // Execute --cmd arguments.