REST API: Add support for the REDIRECT_HTTP_AUTHORIZATION header.

Previously the REST API did not account for server configurations where the Authorization header must be added using ModRewrite. This caused major DUX issues when trying to use custom authentication mechanisms.

Fixes #47077.
Props dshanske, cklosows.

Built from https://develop.svn.wordpress.org/trunk@47239


git-svn-id: https://core.svn.wordpress.org/trunk@47039 1a063a9b-81f0-0310-95a4-ce76da25c4cd