Introduce `map_deep()`, a utility function that recursively maps a callable function to every item in an array or object. Works like `array_walk_recursive()` but works with objects too.
Updates `rawurlencode_deep()`, `urlencode_deep()`, and `stripslashes_deep()` to use `map_deep()`. Introduces `urldecode_deep()` for completeness.
Props wpmuguru, nbachiyski, boonebgorges, MikeHansenMe, chriscct7, realloc, johnbillion
Fixes #22300
git-svn-id: https://develop.svn.wordpress.org/trunk@35252 602fd350-edb4-49c9-b593-d223f7449a82