applets/kicker: port to std::unordered_map to work around a common crash when uninstalling apps

Reason for the change

For some reason QHash doesn't play nicely with std::shared_ptr

https://bugreports.qt.io/browse/QTBUG-129293

Test plan

1. Install GNOME Cheese from the local package manager and Flatpak
2. Add Cheese to Favorites
3. Uninstall Flatpak Cheese
4. Uninstall local Cheese
5. No crash

Screenshots or screen recordings

Bugs fixed

SENTRY: PLASMA-WORKSPACE-NZ0