kcm_filetypes: Save KPart pluginIds rather than desktop file names
Not all KParts provide desktop files anymore. In KF6, we will get rid of then entirely. This allows us to remove the logic in KParts of mapping the desktop file to the plugin.
Not all KParts provide desktop files anymore. In KF6, we will get rid of then entirely. This allows us to remove the logic in KParts of mapping the desktop file to the plugin.