Add support for Object in Udfs

[agavra]

Udfs should be able to support signatures with Object as a parameter that will match anything. This is similar to generics, but does not enforce any specific type across objects. This can be helpful to implement something like TO_STRING(Object val).

[big-andy-coates]

Yep - Object should be like an ANY SQL type

We should also support Object varargs.

Matching rules should mean that Object is only matched if nothing else matches. Where we have methods that contain different amount of Object params, the most specific should be matched.