This caused unnecessary empty <pre> blocks when converting markdown to
HTML, made code blocks too large using QSyntaxHighlighter to highlight
the whole block, and caused assymmetry when rewriting markdown.
Pick-to: 6.3
Fixes: QTBUG-101031
Change-Id: I08016577ccb92edb4afae31d7df3259cb011d5c8
Reviewed-by: Qt CI Bot <qt_ci_bot@qt-project.org>
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>