QTextMarkdownWriter: escape special characters (line or word prefix)

Try to avoid writing anything that the parser would misinterpret.
Escape pre-existing backslashes, but not those that are already escaped.
Optimize maybeEscapeFirstChar() slightly and apply it to every line
of output (except in code blocks), not only to new lines created by
word-wrapping.

Since it would be hard to do this without using regular expressions,
the markdown writer feature now depends on the regex feature.

Fixes: QTBUG-96051
Fixes: QTBUG-122083
Pick-to: 6.7
Change-Id: I8d95366501fd31441829081c668f11a3a3a23fe2
Reviewed-by: Axel Spoerl <axel.spoerl@qt.io>
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>

0 files changed, 0 insertions, 0 deletions