Formatting: In `wp_validate_redirect()`, normalize the path when validating...

Formatting: In `wp_validate_redirect()`, normalize the path when validating the location for relative URLs, to account for Windows paths.

Props peterwilsoncc, rconde, jmmathc, mat-lipe, Sixes, justinahinon, cmagrin, daxelrod, SergeyBiryukov.
Fixes #47980.
Built from https://develop.svn.wordpress.org/trunk@46472


git-svn-id: https://core.svn.wordpress.org/trunk@46270 1a063a9b-81f0-0310-95a4-ce76da25c4cd