kcms/effects: Add "tile"-related keywords

Ultimately the best solution would be to implement
https://bugs.kde.org/show_bug.cgi?id=462722, but that hasn't been done
yet, so for now let's use the existing approach of adding the names of
effects into the keywords list for this KCM to surface those effects at
the system level so e.g. people can find them with KRunner.

BUG: 467279
FIXED-IN: 6.0