Any type (the top type of this type system).
A variable of this type can contain any value, including undefined
and null and any raw JS value. This type supports a very limited set
of Scala operations, the ones common to all values. Basically only
reference equality tests and instance tests. It also supports all
The type java.lang.Object in the back-end maps to AnyType because it
can hold raw JS values (not only instances of Scala.js classes).