[BUGFIX] Respect line breaks in stdWrap.cropHTML

By using the PCRE_DOTALL (/s) pattern modifier in the cropHTML
regular expression for preserving HTML entities the dot in the
pattern will include line breaks.

Resolves: #28741
Releases: 6.1, 6.0, 4.7, 4.6, 4.5
Change-Id: Ifda9e397406dd481b634ded22fd13cac90192118
Reviewed-on: https://review.typo3.org/18219
Reviewed-by: Dmitry Dulepov
Tested-by: Dmitry Dulepov
Reviewed-by: Stefan Neufeind
Reviewed-by: Susanne Moog
Reviewed-by: Philipp Gampe
Tested-by: Philipp Gampe
Reviewed-by: Wouter Wolters
Tested-by: Wouter Wolters
Reviewed-by: Benjamin Mack
Tested-by: Benjamin Mack