feat(interactive-examples): support CSS examples

[caugner]

Summary

Adds support for CSS examples, especially those with multiple choices.

Part of https://github.com/orgs/mdn/discussions/782.

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How did you test this change?

1. Checked out migrate-interactive-examples content branch.
2. Ran yarn dev.
3. Tested especially with these tests:

• http://localhost:3000/en-US/docs/Web/CSS/background-color#try_it
• http://localhost:3000/en-US/docs/Web/CSS/text-align#try_it
• http://localhost:3000/en-US/docs/Web/CSS/color

[LeoMcA]

Lovely work, I opted to "show not tell" with my review, and fixed some things/did some refactoring myself, these can be seen with these diffs:

Mostly fixes/additions of things not implemented yet, notably implementing dark mode: https://github.com/mdn/yari/pull/12664/files/b235911713a9e2f299494bd52d479a471a44b5f5..46cc5847f2dd5d6722f1db32dd02ba76c1041b4b

A pretty major refactor which I think you'd mentioned might be good to do, separating out the choice logic (and tabbed, and console) - achieved it in a perhaps unconventional way (using mixins), but it works nicely: 97fd3a3

Mostly code review changes, notably replacing the bitmask with an array and splitting the click/update events: https://github.com/mdn/yari/pull/12664/files/97fd3a37188151466d70a64c779bcfe3560a89f2..8bcafda92f3e054574dd5eba29f51620bfbc8299

[fiji-flo]

👍 for your changes @LeoMcA