There was a TODO in `crates/settings/src/settings_content/theme.rs` to
make this rename.

This PR is just splitting off this change from
https://github.com/zed-industries/zed/pull/40035 to make reviewing that
one a bit easier since that PR is a bit more involved than expected.

Release Notes:

- N/A

Signed-off-by: Connor Tsui <connor.tsui20@gmail.com>