Prior to this commit, errors unhandled by custom `WebExceptionHandler`
and resulting in an HTTP 500 status would not be logged at ERROR level,
giving no information to developers about the actual exception.

This commit ensures that such exceptions are logged at the ERROR level
with their exception. By the time the exception hits the
`DefaultErrorWebExceptionHandler`, if the response is already committed
or if the exception is due to a client disconnecting, the error is
delegated to Framework support as Spring Boot won't be able to render an
error page as expected.

Fixes gh-15769