- only affects an extreme corner case: user sets `metadata.EditFormatString` then reads
`metadata.DisplayFormatString`
- an extreme case because `EditFormatString` is normally set only when
`DisplayFormatString` is set and, if set, it's to the same value
- happened to see this while updating `CachedDataAnnotationsModelMetadata` for this PR
nit: an -> a in an adjacent XML comment in `CachedDataAnnotationsModelMetadata`
0d92a829ff