[applets/taskmanager] Fix desktop name under wayland when using multiple virtual desktops
Under Wayland QStrings are used to identify virtual desktops, whereas X11 uses uint >0.
The current implementation of the task manager incorrectly displays "On %1(I18N_ARGUMENT_MISSING)" on Wayland rather than the names of the desktop(s) a window is on. Pinned windows also break alignment with other thumbnails.
This MR seeks to fix the following:
- The desktop name(s) subtext is correctly displayed above the thumbnail on both X11 and Wayland
- To fix alignment when a window is pinned. (Currently a pinned window doesn't show any subtext which breaks the alignment with other thumbnails in the group)