[BUGFIX] RTE transformation transforms LF/CR between div and hr into space

Fix the issue and add test cases.

Change-Id: Iff9ce1adc94fdbcf62f3ab4ee25c6c8a3703fe19
Resolves: #26815
Releases: 4.5, 4.6
Reviewed-on: http://review.typo3.org/3861
Reviewed-by: Oliver Hader
Reviewed-by: Tolleiv Nietsch
Tested-by: Tolleiv Nietsch