JSImportCall
JavaScript dynamic import of the form import(arg).
This form is its own node, rather than using something like
JSFunctionApply(JSImport())
because import is not a first-class term in JavaScript.
ImportCall is a dedicated syntactic form that cannot be
dissociated.
trait Serializable
trait Product
trait Equals
class Tree
trait TreeOrJSSpread
class IRNode
class Object
trait Matchable
class Any