.true if the object is a subclass of the specified
class.
Returns .false if the object is not a subclass of the specified
class.
A class is a subclass of a class if the target class is the same as
class or if
class is in the object's direct or mixin
class inheritance chain. For example:
.String~isSubclassOf(.object) --> 1
.String~isSubclassOf(.mutablebuffer) --> 0