[BUGFIX] Add fileSuffix option to GeneralUtility::tempnam()

Currently it is only possible to create a
temporary file with a given prefix and without
any file extension. But for some use-cases you
need a file with a certain file extension.

This patch introduces a new optional parameter to
GeneralUtility::tempnam() to make it possible to add
e.g. a specific extension to the created file.

In addition the occurrences in core, which can benefit
from this, are adapted resulting in less orphaned
temporary files in typo3temp.

Releases: 6.2
Resolves: #54750
Change-Id: I19383bc8f6b387133bff2f4033f05b28e883d427
Reviewed-on: https://review.typo3.org/26650
Reviewed-by: Helmut Hummel
Tested-by: Helmut Hummel
Reviewed-by: Markus Klein
Reviewed-by: Steffen Ritter
Tested-by: Steffen Ritter