[BUGFIX] Clear statcache after writing file contents

To make sure calls to filesize() etc. return correct values the PHP
method clearstatcache() is called in the LocalDriver after contents
were written to a file.

Resolves: #54302
Releases: 6.2
Change-Id: Ia30e519d17aa3cf37856096f1cdac567b5729aec
Reviewed-on: https://review.typo3.org/26278
Reviewed-by: Markus Klein
Reviewed-by: Frans Saris
Reviewed-by: Georg Ringer
Tested-by: Georg Ringer