[FEATURE] Add color scheme switching

This patch adds the ability to switch the active color scheme
using multiple different methods in the Backend User Interface.
The two main methods are a selection of buttons in the user
dropdown at the top right of the Backend, the other one being
a setting present in User Settings.

Additionally, if the "auto" setting (default) is selected, the backend
is automatically using the systems preferred color scheme.

Considering the dark color scheme is still regarded as experimental,
the switching capabilities are currently disabled using a UserTS setting
'setup.fields.colorScheme.disabled'.

Resolves: #104868
Releases: main
Change-Id: I6704fba0930ac579582f1d21dd11368b3509328a
Reviewed-on: https://review.typo3.org/c/Packages/TYPO3.CMS/+/85935


Reviewed-by: Benjamin Franzke <ben@bnf.dev>
Tested-by: Benjamin Franzke <ben@bnf.dev>
Tested-by: Benjamin Kott <benjamin.kott@outlook.com>
Tested-by: core-ci <typo3@b13.com>
Tested-by: Andreas Nedbal <andy@pixelde.su>
Reviewed-by: Andreas Nedbal <andy@pixelde.su>
Reviewed-by: Benni Mack <benni@typo3.org>
Reviewed-by: Benjamin Kott <benjamin.kott@outlook.com>