Rename `color_scheme` -> `theme` (#2677)

Just some theme tidying, renames some things to be more consistent with
our planned naming conventions going forward.

Release Notes:

- N/A (No public facing changes)
76af424d79Nate Butler committed on 7/4/2023, 3:56:30 PM· committed by GitHubparentsc5a42c3f461a70
18 files changedLine totals unavailable