create Lit specific polyfill plugin

[thescientist13]

Type of Change

• New Feature Request
• Documentation / Website
• Improvement / Suggestion
• Bug
• Other (please clarify below)

Summary

As part of the Lit@2 upgrade, one of the things we needed to add was support for Lit specific polyfills, as seen in #719 . As we shouldn't have anything library specific in the core CLI and so should move this logic out into a plugin for those who want to use Lit + Puppeteer.

Details

So effectively we just need to make a new (resource) plugin to isolate the Lit specific checks and polyfill add / cleanup from plugin-standard-html. We should also make sure to add some tests here as well.

We should also make sure to document in its README the relationship to Lit / SSR as well as our standard plugin-polyfill.

We should also clean up TODOs from #974 related to Lit Polyfill popping up and is hardcoded into the Node Modulesresource plugin.

This could almost be considered a breaking change, so best to do it pre 1.0.0

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This is actually part of the polyfills plugin, so not sure if that's OK for now? 🤔

In either #955 and #1197 it will get moved out of the CLI at least.

[thescientist13]

I wonder if this should just get bundled with the (eventual) renderer work in #710 ?