Symfony version(s) affected: 4.4, 5.0

Description
When an exception occurs before the kernel.request event (for example during Kernel::boot), then the exception is dumped with full stack trace, also in prod.

How to reproduce
Set APP_ENV=prod and throw an exception in Kernel::boot.

Possible Solution
Initialize Symfony\Component\ErrorHandler\ErrorHandler::$scopedErrors to 0 instead of 0x1FFF.

Or alter the construction of Symfony\Component\ErrorHandler\ErrorRenderer\HtmlErrorRenderer not to rely on $this->scopedErrors being 0 to determine if the $debug parameter should be true.
Currently it's initialized as follows: new HtmlErrorRenderer(0 !== $this->scopedErrors)
(Symfony\Component\ErrorHandler\ErrorHandler line 700)

$scopedErrors is currently set to 0 (when kernel.debug is false) by calling the Symfony\Component\ErrorHandler\ErrorHandler::scopeAt method in Symfony\Component\HttpKernel\EventListener\DebugHandlersListener::configure on line 96, which is trigged in the kernel.request event.