Add samples for flatten, unzip functions

libraries/stdlib/samples/test/samples/collections/sequences.kt

@@ -242,6 +242,32 @@ class Sequences {
             assertPrints(even, "[0, 2, 8, 34]")
             assertPrints(odd, "[1, 1, 3, 5, 13, 21]")
         }
+
+        @Sample
+        fun flattenSequenceOfSequences() {
+            val sequence: Sequence<Int> = generateSequence(1) { it + 1 }
+            val sequenceOfSequences: Sequence<Sequence<Int>> = sequence.map { number ->
+                generateSequence { number }.take(number)
+            }
+
+            assertPrints(sequenceOfSequences.flatten().take(10).toList(), "[1, 2, 2, 3, 3, 3, 4, 4, 4, 4]")
+        }
+
+        @Sample
+        fun flattenSequenceOfLists() {
+            val sequence: Sequence<String> = sequenceOf("123", "45")
+            val sequenceOfLists: Sequence<List<Char>> = sequence.map { it.toList() }
+
+            assertPrints(sequenceOfLists.flatten().toList(), "[1, 2, 3, 4, 5]")
+        }
+
+        @Sample
+        fun unzip() {
+            val result = generateSequence(0 to 1) { it.first + 1 to it.second * 2 }.take(8).unzip()
+
+            assertPrints(result.first.toList(), "[0, 1, 2, 3, 4, 5, 6, 7]")
+            assertPrints(result.second.toList(), "[1, 2, 4, 8, 16, 32, 64, 128]")
+        }
     }
 
 }