Interface representing a Tail Call. This is a package of information passed back by a called
instruction to its caller, representing a call (and its arguments) that needs to be made
by the caller. This saves stack space by unwinding the stack before making the call.
Process this TailCall (that is, executed the template call that is packaged in this
object). This may return a further TailCall, which should also be processed: this
is the mechanism by which a nested set of recursive calls is converted into an iteration.
a further TailCall, if the recursion continues, or null, indicating that the
recursion has terminated.