Separate monoidal part of strict layers

[jisantuc]

Overview

This PR separates the monoidal part of StrictLayers -- the separate collections of geometries -- from the... I guess "metadata", you know, the other part.

It's useful, e.g., if you're getting geometries from somewhere and trying to combine everything into a vector tile layer. The collections of geometries form a lawful monoid, but StrictLayer as it's currently implemented does not.

Checklist

• ./CHANGELOG.md updated, if necessary. Link to the issue if closed, otherwise the PR.
• Module Hierarchy updated, if necessary
• docs guides update, if necessary
• New user API has useful Scaladoc strings
• Unit tests added for bug-fix or new feature -- already tested, just a small reorganization

Demo

I would have used this here instead of hand-rolling a special Monoid for strict layer for each z/x/y triple

Notes

I'd like to prove this is a lawful monoid with discipline -- e.g. https://github.com/raster-foundry/raster-foundry/blob/develop/app-backend/datamodel/src/test/scala/ScopeSpec.scala#L126. It's pretty easy, but it would require new testing deps and also Arbitrary instances for everything going up the dependency chain from the MVTFeatures, which seems like a lot for what is in practice a very fancy Map[String, Seq[A]].

[pomadchin]

Hey James! Thanks for the PR; we haven't had a chance to look into it though.

One minor thing here, could you sign ECA please to make Eclipse license checker happy?

After that you'd need to add a sing-off footer into the commit via git commit --amend -s && git push origin -f feature/js/separate-monoidal-part-of-vt
If you have more than a single commit in the PR than all commit messages should have a sign off fitter

P.S. git commit --amend -s adds the necessary footer into the commit message that is required for the successful license check.

P.P.S. gz with your first official PR 🎉 🎉