[Sync-EN] Document the exception handler stack behavior of PHP 8.3.0 and 8.3.5

[lacatoire]

Syncs reference/errorfunc/functions/restore-exception-handler.xml and reference/errorfunc/functions/set-exception-handler.xml with php/doc-en#5222.

Both pages gain the note and the changelog describing the handler stack behaviour:

• As of PHP 8.3.0 the engine unsets the active exception handler before invoking it, so an exception thrown by the handler is not passed back to it, and set_exception_handler() called from within a handler reports no previously defined handler.
• As of PHP 8.3.5 the engine also pushes the handler it is about to invoke onto the stack, so restore_exception_handler() called from within a handler re-installs the handler that is currently running; restoring the one active before it takes two calls.
• The running handler is re-installed automatically on return, but only if no handler is active at that point; a handler that touches the stack itself is left in charge of it, which is why modifying the exception handler from within itself is discouraged.

Both see-also simplelists are no longer wrapped in a para, as upstream.

EN-Revision bumped to 1cc803aaa07ac94ce8e3bfdf56f4b9ddd23326d3 on both files.

Fixes: #1695