Issue #2501319 by joelpittet, cwells, stefan.r, YesCT, nlisgo, Cottser,...

Issue #2501319 by joelpittet, cwells, stefan.r, YesCT, nlisgo, Cottser, cmanalansan, dawehner, xjm, alexpott, josephdpurcell: Remove SafeMarkup::set() in Error::renderExceptionSafe() and _drupal_log_error() and improve backtrace formatting consistency in _drupal_log_error(), Error::renderExceptionSafe(), and DefaultExceptionSubscriber::onHtml()