[FEATURE] Render closures with DebuggerUtility::var_dump()

DebuggerUtility::var_dump() is now able to render closures. The source
code of a closure is now rendered in the output.

Resolves: #76458
Releases: master
Change-Id: Ie9a8e84250a19ee64e3e7d4cb0fbbc078c468bfa
Reviewed-on: https://review.typo3.org/48453


Reviewed-by: Joerg Boesche <typo3@joergboesche.de>
Tested-by: Joerg Boesche <typo3@joergboesche.de>
Reviewed-by: Susanne Moog <typo3@susannemoog.de>
Tested-by: Susanne Moog <typo3@susannemoog.de>