Feature/issue 709 custom render plugin

[thescientist13]

Related Issue

#709 / #710

Summary of Changes

1. Introduced a renderer plugin API
2. Introduced a Lit renderer plugin
3. Added headers to Resource plugins for optimize to support both static (file) and server (route) contexts
4. Added documentation for custom render plugin API

TODO

1. make greenwood implementation a plugin
2. Investigate how to delineate between render (server) vs prerender (client) and understand how to custom render an SSG site (w/ hydration?)
3. html plugin refactoring
4. Tests
5. Docs
6. Remove demo code

Thoughts / Questions

1. Should we use VM context for Lit plugin?
   • It is experimental, so maybe no, just try and contain it all in the Worker? (worker should provide isolation, right?)
   • FWIW, I think because we are in a Worker though (for reloading ESM in development), we are able to avoid issues like this, so maybe these are equivalent? (Or at least use Workers until VM context gets unflagged)
     • [ssr] Lit SSR breaks Sass with polyfill lit/lit#2393
     • [ssr] SSR rendering in NextJS lit/lit#2391
2. Ongoing Investigations (merge into the release branch issue tracking list)
   • static rendering w/ custom renderer, e.g. www/ + Lit (just have experimental support right now) and define patterns / practices
   • hydration support for SSG & SSR (how do we get the data in an SSG context though... ?)
   • streaming support for HTML via generators would be awesome!

[thescientist13]

Good catch on the call @hutchgrant 🔍 👀

I was trying to be a bit too clever maybe by having an option for SSR routes to be rendered by a custom renderer (e.g. Lit) AND also puppeteer, but that seems excessive since the whole point of a custom renderer is to avoid that overhead. Puppeteer was basically giving us its own HTML instead of the nice HTML that Lit gave us with declarative shadow DOM and all the nice hydration markers.

Verified it works as expected now and also updated that spec to test the affirmative (explicit name matches) as opposed for testing the negative (absence of default placeholder text). Thanks! 🤝