Implements Reflame's new testing features. :)

Currently the only kind of test available are component screenshot
tests, where you supply a React component/element, and we'll take a
screenshot of it every time you push a commit (and later diff it against
the last known good version, skip it if its dependencies hasn't changed,
etc).

There are two ways to write tests at the moment:

1. Export a React component or element from any module with a _test
postfix
([examples](https://github.com/highlight/highlight/pull/6699/files#diff-82085b66646a6df6fc80fb2efc545a69271e0f7f28bbb03c6428d44fdaa2bdbbR33)
[here](https://github.com/highlight/highlight/pull/6699/files#diff-0073669d5601b1c655cb637e2d52832d1cce7426584d02315d6df24cc423dc16R20)).
Anything with a _test postfix will be eliminated in non-testing builds,
and then a dead code elimination pass will be performed, so in theory
there shouldn't be leakage of testing-only deps from this.

2. Export a React component or element with any name (except `default`)
from a `*.stories.{ts|tsx|js|jsx}` file. This enabled through the
storybook compat config, and is why all of the stories in
`@highlight-run/ui` are being picked up automatically.

Let me know what you think!

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