Summary:
Now all font selection dialogs use KFontChooserDialog (from KWidgetAddons),
bump KF5 minimum required version to 5.69.0.

KFontChooserDialog has some pros over QFontDialog:
 - If the font to pre-select in KFontChooser doesn't have the styleName
   property set, the dialog will try and select the correct style (usually
   that works); this is useful since we want to save/load fonts with
   "Regular"-like styles without setting that property so that setBold(true)
   can work properly
- Fractional font sizes, e.g. 10.5 pt (QFontDialog only supports int)
- KFontChooserDialog will discard "Regular"-like styleName prop. after
  the user has selected a font, which means less workarounds in the fonts
  KCM code.

Do not check for immutability:
 - The setters generated by KConfig already do that
 - The QML FontWidget check for immutability and disable the relevant
   font widget

adjustAllFonts() doesn't take any args, change the qml code accrodingly.

Test Plan: The fonts KCM still works.

Reviewers: #plasma, davidedmundson, broulik, meven, cfeck, bport

Reviewed By: bport

Subscribers: plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D27808