hands_over to covering

BUR #8276 has been approved by @evazion.

create alias hands_over_eyes -> covering_eyes
create alias hands_over_mouth -> covering_mouth
create alias hands_over_ears -> covering_ears

For both eyes and mouth, we have a much larger "covering" tag and a smaller "hands over" tag with no wiki to indicate a difference, so I don't see a reason not to merge them. Ears is for findability.

We also have hand over own mouth and hand_over_eye.

The first implies covering mouth already, so it probably makes sense to alias the plural forms to covering* and imply the single variant to them.

The bulk update request #8276 (forum #202421) has been approved by @evazion.