[BUGFIX] Allow target attribute for more doctypes

The target attribute for links is allowed according to w3c documentation
in more doctypes than xhtml frameset and html5.

Change-Id: Id4110399dec1c1f1d0a4d69342440021837b51a9
Resolves: #37710
Releases: 6.2, 6.1, 6.0
Reviewed-on: https://review.typo3.org/22224
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters