Introduce R::I.LastFromIterator

Return the last value generated from an iterator, or IterationEnd
for an empty iterator. Generalised from List.tail() functionality.
To be used later for Str.match(/./, :nth(*))

src/core/Any-iterable-methods.pm

@@ -1898,23 +1898,13 @@ Did you mean to add a stub (\{...\}) or did you mean to .classify?"
 
     proto method tail(|) { * }
     multi method tail(Any:D:) is raw {
-        nqp::stmts(
-          (my $result := IterationEnd),
-          nqp::if(
-            (my $iter := self.iterator).is-lazy,
-            Failure.new(X::Cannot::Lazy.new(:action<tail>)),
-            nqp::stmts(
-              nqp::until(
-                nqp::eqaddr((my $pulled := $iter.pull-one),IterationEnd),
-                ($result := $pulled)
-              ),
-              nqp::if(
-                nqp::eqaddr($result,IterationEnd),
-                Nil,
-                $result
-              )
-            )
-          )
+        nqp::if(
+          nqp::eqaddr((my $pulled :=
+            Rakudo::Internals.LastFromIterator(self.iterator,'tail')),
+            IterationEnd
+          ),
+          Nil,
+          $pulled
         )
     }
     multi method tail(Any:D: Int(Cool) $n) {

src/core/Rakudo/Internals.pm

@@ -368,6 +368,22 @@ my class Rakudo::Internals {
         }.new(iterator, n, action, $full)
     }
 
+    # Return the last value of an iterator (if any)
+    method LastFromIterator(\iterator, $action) is raw {
+        nqp::if(
+          iterator.is-lazy,
+          X::Cannot::Lazy.new(:$action).throw,
+          nqp::stmts(
+            (my $result := IterationEnd),
+            nqp::until(
+              nqp::eqaddr((my $pulled := iterator.pull-one),IterationEnd),
+              ($result := $pulled)
+            ),
+            $result
+          )
+        )
+    }
+
     # Iterate over a source iterator and an iterator generating index values
     # from a given offset.  Optionally, call block if an out-of-bounds index
     # value is obtained, or simply return Nil for out of bounds index values