Improve localization for `WP_Date_Query` error strings.

* Don't create an extra variable for the string when it's only used once.
* Avoid using `<code>` HTML tags inside of translatable string.
* Improve data types and escaping on sprintfed values.

Props dd32.
Fixes #25834.

git-svn-id: https://develop.svn.wordpress.org/trunk@30300 602fd350-edb4-49c9-b593-d223f7449a82