Export autoload discover function and support shadow roots

[jaredcwhite]

This allows for a discover(this.shadowRoot) call within a consumer's web component to opt-into autoloading. Otherwise, if someone has built a component which includes a Shoelace component in the component's shadow DOM, autoloading won't work.

(Note: this doesn't add a mutation observer, so it's a one-time discovery. Most component shadow trees are pretty stable I imagine, so I think that's fine, but if it feels too much like a potential gotcha, we could consider opting-in to a mutation observer for the tree.)

[vercel]

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Name	Status	Preview	Updated
shoelace	✅ Ready (Inspect)	Visit Preview	Mar 11, 2023 at 5:39PM (UTC)

[claviska]

I figured this would come pretty quickly. The reason I held off is because we probably don't want to encourage autoloading in custom elements in the majority of cases. In fact, the only scenario we probably do want to support is when folks build their apps using Lit, FAST, or similar libraries as a framework.

In other words, they use a custom element app container, a custom element router, etc. and because of that, pretty much everything in their app happens to live in a single shadow root. I don't think it makes sense to use an autoloader for independent, third-party components, however.

I'm happy to merge this, but I'm not sure where to document it (or even if we should just yet). Any thoughts on where that should live in the docs?

[claviska]

Regarding the mutation observer — I'm with you. It's only a few lines to setup your own if you really need it, but I'd be OK with exporting a factory function that removes the boilerplate if this becomes a popular request.

[jaredcwhite]

I'm not sure where to document it (or even if we should just yet).

Yeah, I'm waffling on that too. I think it's fine as an easter egg of sorts for now, and see if people even end up needing that functionality all that often.