[feat] Set up an element query approach in the PFElement base class

[mwcz]

eq.js adds element queries so that elements can respond to their own size, rather than the page's size.

https://github.com/Snugug/eq.js/

Evaluate eq.js performance, features, etc for inclusion within RHElements.

At first glance, it looks small enough (1.1kb min+gzip) and useful enough that I think making it available to all RHElements is a good idea.

[starryeyez024]

yay! Such a small and powerful library.

[chrisdo1]

@mwcz seems like you're on board with adding this to the repo. With your permission I will include it in the hide-show component I'm working on now.

[mwcz]

@chrisdo1 That's fine for a proof of concept, but if we do include eq.js it needs to be in the RHElement base class, with an API for components to opt-in to using it.

[castastrophe]

I renamed this to be a bit more open-ended because it would be more lightweight to set up an EQ built into the base class rather than use a library. We can evaluate the EQ.js syntax for if we want to do something similar though.