[FEATURE] TS-list: allow to unique, reverse and sort

Add missing, basic list-functionality for TypoScript.
Also splits out the TS-operator-functions into a
separate function and adds unit-tests.

Resolves: #45091
Releases: 6.1
Change-Id: I2ff425845681494053dc56b785ebd0064f100ed6
Reviewed-on: https://review.typo3.org/17939
Reviewed-by: Philipp Gampe
Tested-by: Philipp Gampe
Reviewed-by: Christian Kuhn
Tested-by: Christian Kuhn