lib/options: lib/neovim-plugin: Add lazyLoad option to plugins

[psfloyd]

This PR works on a solution for the issue #421.

Already implemented

• Adding mkLazyLoadOption to generate lazyLoad options for plugins.
• Adding and implementing a lazy-loading mechanism using lz.n
• Conditionally enabling lazy or regular loading depending on user settings in mkNeovimPlugin

Planned

• For plugins that do not callSetup, extract extraConfigLua from extraConfig.
• Integrate with mkVimPlugin

[MattSturgeon]

Thanks for working on this, I'm sure many people will be pleased to see progress here!

I haven't taken a proper look yet, but I left some comments below.

• Would it be possible to extract parts of this into smaller PRs?
  • E.g. initializing plugins.lz-n could be its own PR.
• Would it be possible for mkLazyLoadOption to work with either plugins.lz-n or plugins.lazy based on user preference?

[psfloyd]

Thank you for your review!

• Would it be possible to extract parts of this into smaller PRs?

  • E.g. initializing plugins.lz-n could be its own PR.

Yes, I am going to make a PR for lz-n, and use that PR as base for the lazyLoad options

• Would it be possible for mkLazyLoadOption to work with either plugins.lz-n or plugins.lazy based on user preference?

Yes, I think it should be possible. I could add a backend option to select which one to use. But I don't think it should be set on a per plugin basis.
Should we add a global config.lazyLoader option with global parameters for lazy-loading?
On that namespace we could add an enable option and apply it to the corresponding backend.