[TASK] Split xdebug.max_nesting_level into two error levels

The recommended xdebug.max_nesting_level was raised from 250 to
400 with issue #59391. Since the core itself usually works fine
with 250 and more is usually only needed for extensios with
deeply nested partials in fluid for example, the check is now
split to two error levels: Below 250 throws error level warning,
below 400 throws only a warning level warning.

Resolves: #61523
Related: #59391
Releases: master, 6.2
Change-Id: I366a97fe8077a389fff7f03935ad5b89d1469bc9
Reviewed-on: http://review.typo3.org/32782
Reviewed-by: Anja Leichsenring <aleichsenring@ab-softlab.de>
Tested-by: Anja Leichsenring <aleichsenring@ab-softlab.de>