Make it easier to define userland "components"

[armanbilge]

See also:

• Should Modifier be a typeclass? #207
• A first-class DSL for working with class and other attributes #205

Consider this Laminar-style example:

def MyComponent(mods: Mod[HtmlElement]*) = 
  div(
    cls := "decoration",
    mods
  )

At the moment this wouldn't work great with Calico, because modifiers are typeclass-based (#207). Another issue is that if the caller of MyComponent wants to add additional cls values, it would override the cls := "decoration" (#205). It doesn't compose well.

The composition issue in particular bugs me, since it's not just about the class attribute but basically any attribute. It's too easy to mess up the "component"'s internals when doing things externally.

Hence why I say "component", because it's not really well encapsulated. I feel like the answer might be #37: that we should make it easy to define true Web Components, that have proper encapsulation of their internals. Web Components specifically solves this issue of encapsulation.