Update styled-components dependencies

[dgreif]

I recently updated most of the base-level dependencies (#1292). One that I elected to skip was styled-components, which has a major release with big perf improvements. I tried updating, but most of the snapshots needed to be updated and there were other issues with the tests. I don't think the changes are actually significantly breaking, but this bump should be handled separate from other dependency bumps so that it gets the proper attention it needs.

[moatorres]

My best guess is that the patch below is the origin of the issue.

From sc releases:

v5.2.0-test.10 + v5.2.0

Rework how components self-reference in extension scenarios (see #3236); should fix a bunch of subtle bugs around patterns like & + &

You might want to check issues 3236, 3265 and 3401 from styled-components repo.

[colebemis]

Looks like there is an open issue with jest-styled-components (styled-components/jest-styled-components#276) that breaks our snapshot tests when we upgrade to v5.

I'd argue that this is a low priority for us to fix right now because, since styled-components is a peer dependency, consumers of Primer React can use v5 in their application without any changes on the Primer React side (Memex already uses v5).

[colebemis]

Closing this for now until we determine if we want to use styled-components long term: https://github.com/github/primer/issues/203