[FEATURE] Add uri/link to backend route ViewHelper

Since unified URL routing is in place for TYPO3 v9 now,
a new pair of linking to routes is added.

Change-Id: Ied1a67aee173a9a1dc00eaadc9676ded1276076f
Resolves: #75161
Releases: master
Reviewed-on: https://review.typo3.org/47306


Reviewed-by: Benni Mack <benni@typo3.org>
Tested-by: Benni Mack <benni@typo3.org>
Tested-by: TYPO3com <no-reply@typo3.com>
Reviewed-by: Susanne Moog <susanne.moog@typo3.org>
Tested-by: Susanne Moog <susanne.moog@typo3.org>