[Image Wallpaper] Make color picker visible for all positioning mode.
Summary:
If user is using svg wallpaper with opaque area, then this allows users to fill opaque area with color.
BUG: 351012
Reviewers: Plasma, bshah
Reviewed By: Plasma, bshah
Subscribers: bshah, broulik, plasma-devel
Projects: Plasma
Differential Revision: https://phabricator.kde.org/D1008