The `WP_Shutdown_Handler` name plus related function names were premature when originally committed, as there can be multiple shutdown handlers in PHP, and WordPress makes use of that feature. This changeset modifies the name to a more appropriate `WP_Fatal_Error_Handler`, and related to that changes the following names:
* The drop-in to override the handler is now called `fatal-error-handler.php`.
* The internal function `wp_register_premature_shutdown_handler` is now called `wp_register_fatal_error_handler()`.
In addition to these naming changes, a new constant `WP_DISABLE_FATAL_ERROR_HANDLER` is introduced that can be set in `wp-config.php` to entirely disable the fatal error handler. That constant's value is and should be accessed indirectly via a new `wp_is_fatal_error_handler_enabled()` function and is filterable via a new `wp_fatal_error_handler_enabled` hook. Note that disabling the fatal error handler will skip the new functionality entirely, including the potentially used `fatal-error-handler.php` drop-in.
The new set of constant, filter and function provide for an easier-to-use mechanism to disable the fatal error handler altogether, rather than requiring developers to implement a drop-in for purely that purpose.
Props afragen, flixos90, joyously, knutsp, markjaquith, ocean90, schlessera, spacedmonkey.
Fixes#46047. See #44458.
git-svn-id: https://develop.svn.wordpress.org/trunk@44674 602fd350-edb4-49c9-b593-d223f7449a82
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