Bootstrap/Load: Support WP_Error and $args passed to wp_die() consistently in all handlers.

Prior to this change, each `wp_die()` handler had their own logic for how to parse arguments, causing inconsistencies and even breakage because the arguments possible to pass to `wp_die()` depended on the request context. Passing a `WP_Error` as `$message` for example used to be only support by the default handler, but not the AJAX and XML-RPC handlers.

With the fatal error protection, plus the new `wp_die()` handlers related to that, improving this support and compatibility has become more significant. Therefore this changeset introduces a private `_wp_die_process_input()` function that handles all function parameters consistently.

Props spacedmonkey, flixos90, schlessera.
Fixes #45933. See #44458.

Built from https://develop.svn.wordpress.org/trunk@44666


git-svn-id: http://core.svn.wordpress.org/trunk@44497 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/version.php

@@ -13,7 +13,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '5.1-beta1-44665';
+$wp_version = '5.1-beta1-44666';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.