panelconfiguration: use radio buttons for mututally exclusive items
requested to merge ngraham/plasma-desktop:radiobuttons-for-mutually-exclusive-items-on-more-settings-panel-popup into master
Previously we used conjoined buttons, but in the PC3 port to be compatible with Qt6, we lost the conjoined appearance, making the options look a lot less mutually exclusive than they used to.
To remedy this, instead use Radio Buttons, which are the most original and recognizable UI controls to denote mutually exclusive actions.
| Before | After |
|---|---|
 |
 |