Scrolling a settings page horizontally feels awkward most of the time.
This (optionally) lets the dialogue resize when it is opened so that
horizonal scrolling becomes unnecessary.
Things I am uncertain about:
- Placement of the "FittingScrollArea" class above the function where it is used, and its name.
- "fitContentHorizontally" is off by default in "KConfigDialog::addPage()" so existing code using the function not break because of this change.
This change was discussed in Phabricator Differential D16048.