[!!!][TASK] Make the TYPO3 Backend responsive and remove ExtJS Viewport

A responsive CSS viewport replaces the legacy the ExtJS
component TYPO3.Viewport.

Resolves: #52877
Releases: master
Change-Id: I6d9c6c4e32cf67df3eeb072448e6b4322853d10c
Reviewed-on: https://review.typo3.org/47637


Reviewed-by: Andreas Fernandez <typo3@scripting-base.de>
Tested-by: Andreas Fernandez <typo3@scripting-base.de>
Reviewed-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: Wouter Wolters <typo3@wouterwolters.nl>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>