[BUGFIX] Handle variadic arguments in Extbase DebuggerUtility

Variadic arguments are optional but do not have a default value, thus
properly check this.

Also render the variadic operator ("...") in the output.

Resolves: #82956
Releases: master, 8.7
Change-Id: I10e3528d9cffcdd03ae4711b139898f569ac3775
Reviewed-on: https://review.typo3.org/54600


Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Alexander Schnitzler <review.typo3.org@alexanderschnitzler.de>
Tested-by: Alexander Schnitzler <review.typo3.org@alexanderschnitzler.de>
Reviewed-by: Andreas Fernandez <typo3@scripting-base.de>
Tested-by: Andreas Fernandez <typo3@scripting-base.de>