Move responsive position utilities from marketing to core

[sophshep]

This PR moves the responsive position styles (and their docs) from primer-marketing into primer-core.

This first came up as a need in this GitHub PR, but I suspect that as we're doing more and more responsive work in the product that these will be valuable in primer-core in the future.

/cc @primer/ds-core @jonrohan

[mdo]

This might not be the best time to ask this, but I'd love to see these utilities broken apart more. While working on the Blog migration awhile back, many of these weren't useful for a basic layout and this one file mixes utilities that affect inline-ish elements (vertical-align), text direction, and position. None of these aside from position screams "layout" to me, but admittedly my experience is limited to Primer 9.x several months ago. Dunno what else has changed since then or if our approach in the Blog even changed since then.

[shawnbot]

I feel good about this, but I'm on the fence about whether this is a minor or major change. On one hand, moving styles feels major to me because it "breaks" people's assumptions about what CSS will be output when the @import certain SCSS files. On the other hand, is there any possible use cae for primer-marketing without primer-core?

[sophshep]

is there any possible use case for primer-marketing without primer-core?

I can't think of any projects where I've used primer-marketing without primer-core.

[shawnbot]

Well, I went searching, and here's what I found:

• Most search hits for dependencies + primer-marketing turned up what appear to be forks of government.github.com that all depend on the same versions of primer-core and primer-marketing, so yay!
• Except! githubuniverse.com appears to depend on primer-marketing but not primer-core. See: package.json
• SO MANY PEOPLE HAVE node_modules COMMITTED TO GIT! 😱

[shawnbot]

@sophshep I changed the base branch of this so that it'll merge (eventually) into #498, but that branch is itself way out of date with master. Let's take a look at getting this wrapped up next week.

[shawnbot]

@sophshep how would you feel about merging #545 into this and using that pattern here, too?

[shawnbot]

Heads up @mdo: I added this variable so that responsive position utilities can be customized. For instance, if you only use relative or absolute positioning, you can do something like:

$responsive-positions: (relative, absolute);
@import "primer-core/index.scss";

And instead of 20 position utilities, you'd get 10.

[shawnbot]

@sophshep I've made some changes and am approving for inclusion in v11: #498. Thank you for this! 🎉

[shawnbot]

This is actually pretty cool: removing primer-marketing-utilities/docs/layout.md caused the /utilities/layout page to disappear, which triggered a failing test. I had to mark that URL as having moved in order to get it passing again.