Rename argument for Expr pullAll/pushAll methods
Rename addManyToSet to addEachToSet and remove recursive merging

addEachToSet() more clearly communicates that we're using the $each operator, and will be consistent when pushEach() is added later. Leave addManyToSet() in place, but deprecate it in the documentation.

The recursive merging in addManyToSet dates back to: doctrine/mongodb-odm@59a2da0bf7a53075f9d93b9b1327abccf561c1d1. This could be problematic if multiple calls to addManyToSet() had arrays as the values; they could be merged together in PHP. The new behavior will just overwrite the existing value in the new object, like other update operators.