Support multiple 'status' values in `WP_Comment_Query`.

This change required turning the SQL concatenation into the generation of an
array, for greater flexibility.

Props karpstrucking, ebinnion.
Fixes #29612.

git-svn-id: https://develop.svn.wordpress.org/trunk@30084 602fd350-edb4-49c9-b593-d223f7449a82