Enable the checkUnexported option in the krtequals custom linter

[timflannagan]

See #13091 which replaces our in-tree krtequals version in favor of a standalone repo. I added the checkUnexported option to the standalone repo yesterday, which filled a critical gap in the in-tree implementation where unexported fields were skipped in the linter. This is a problematic gap since most structs don't need to export fields, and therefore those unexported fields are skipped when analyzing Equals implementations.

We should enable that linter option & burn down the linter violations (iirc, it's 10+).