[FEATURE] Improve thumbnail quality on FE

Quality of thumbnails is not satisfying on the FE.
This is caused by the task ProcessedFile::CONTEXT_IMAGEPREVIEW
which render optimised thumbnails however with poor quality.

The task is replace by
ProcessedFile::CONTEXT_IMAGECROPSCALEMASK on the FE only.

Change-Id: I51ba4f634b9e18bacd09e043378265893a777435
Releases: 2.0.0
Resolves: #54215
Reviewed-on: https://review.typo3.org/25967
Reviewed-by: Fabien Udriot
Tested-by: Fabien Udriot