[TASK] Introduce Source Sans Pro and drop Share Font

To improve readability in the backend, Source Sans Pro typeface is now
introduced and replaces the Share Font.

Resolves: #82410
Releases: master
Change-Id: Id9a71b37bb41ff0e0b7fb514e62aebd380ff3d2b
Reviewed-on: https://review.typo3.org/54063


Tested-by: Stefan Neufeind <typo3.neufeind@speedpartner.de>
Tested-by: Joerg Kummer <typo3@enobe.de>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Christian Kuhn <lolli@schwarzbu.ch>
Tested-by: Christian Kuhn <lolli@schwarzbu.ch>
Reviewed-by: Andreas Fernandez <typo3@scripting-base.de>
Tested-by: Andreas Fernandez <typo3@scripting-base.de>
Reviewed-by: Jan Helke <typo3@helke.de>
Tested-by: Jan Helke <typo3@helke.de>
Reviewed-by: Nathan Boiron <nathan.boiron@gmail.com>
Tested-by: Nathan Boiron <nathan.boiron@gmail.com>
Tested-by: Patricia Tiedemann <pixelaeffchen@googlemail.com>
Reviewed-by: Simon Praetorius <simon@praetorius.me>
Tested-by: Simon Praetorius <simon@praetorius.me>
Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>