Add dark snapshots to xl breakpoint visual regression tests

[obulat]

Fixes

Related to #4305 by @zackkrida

Description

This PR adds the dark snapshots for xl tests by setting the useColorMode to true when the snapshot name contains -xl string.

Testing Instructions

The CI should pass. Only the dark snapshots should be added.

Checklist

• My pull request has a descriptive title (not a vague title likeUpdate index.md).
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  PRs) or the media properties generator (ov just catalog/generate-docs media-props
  for the catalog or ov just api/generate-docs for the API) where applicable.

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[zackkrida]

Breakpoints are a nice, organic way to split up these PRs. Good idea 😄. All of the snapshots look goo here, and of course we'll replace the homepage once that work is done (which will actually be a nice way of testing the dark mode snapshots).