add a `loaded_*` variable in case `after/plugin/` sourced twice

[aceforeverd]

In my stupid neovim setup, I use lazy.nvim with loadplugins = true, to use packages as well. Yet problems is plugins managed by lazy will sourced twice, so for plugins like cmp-path, I got the exact same complete entries, twice.

The PR is mainly for discussion (I guess ?), maybe there is a better solution, or just say bye to packages.

Thanks

[aceforeverd]

solved, adding the InsertEnter event should fix