Rename sequence and iterator builder functions and their scope class

This introduces new functions instead of the existing sequence builders:
- `sequence` instead of `buildSequence`
- `iterator` instead of `buildIterator`
- `SequenceScope` instead of `SequenceBuilder`

The old functions were deprecated with error and made inline-only, and `SequenceBuilder` has been
made a deprecated typealias to `SequenceScope`.

Move sequence builders to `SequencesKt` facade class.

Replace sequence builder usages in stdlib and samples.

#KT-26678

libraries/stdlib/test/coroutines/SequenceBuilderTest.kt

@@ -10,7 +10,7 @@ import kotlin.test.*
 class SequenceBuilderTest {
     @Test
     fun testSimple() {
-        val result = buildSequence {
+        val result = sequence {
             for (i in 1..3) {
                 yield(2 * i)
             }
@@ -23,7 +23,7 @@ class SequenceBuilderTest {
 
     @Test
     fun testCallHasNextSeveralTimes() {
-        val result = buildSequence {
+        val result = sequence {
             yield(1)
         }
 
@@ -44,7 +44,7 @@ class SequenceBuilderTest {
 
     @Test
     fun testManualIteration() {
-        val result = buildSequence {
+        val result = sequence {
             yield(1)
             yield(2)
             yield(3)
@@ -72,7 +72,7 @@ class SequenceBuilderTest {
 
     @Test
     fun testEmptySequence() {
-        val result = buildSequence<Int> {}
+        val result = sequence<Int> {}
         val iterator = result.iterator()
 
         assertFalse(iterator.hasNext())
@@ -84,10 +84,10 @@ class SequenceBuilderTest {
     @Test
     fun testLaziness() {
         var sharedVar = -2
-        val result = buildSequence {
+        val result = sequence {
             while (true) {
                 when (sharedVar) {
-                    -1 -> return@buildSequence
+                    -1 -> return@sequence
                     -2 -> error("Invalid state: -2")
                     else -> yield(sharedVar)
                 }
@@ -116,10 +116,10 @@ class SequenceBuilderTest {
     @Test
     fun testExceptionInCoroutine() {
         var sharedVar = -2
-        val result = buildSequence {
+        val result = sequence {
             while (true) {
                 when (sharedVar) {
-                    -1 -> return@buildSequence
+                    -1 -> return@sequence
                     -2 -> throw UnsupportedOperationException("-2 is unsupported")
                     else -> yield(sharedVar)
                 }
@@ -140,7 +140,7 @@ class SequenceBuilderTest {
     @Test
     fun testParallelIteration() {
         var inc = 0
-        val result = buildSequence {
+        val result = sequence {
             for (i in 1..3) {
                 inc++
                 yield(inc * i)
@@ -152,7 +152,7 @@ class SequenceBuilderTest {
 
     @Test
     fun testYieldAllIterator() {
-        val result = buildSequence {
+        val result = sequence {
             yieldAll(listOf(1, 2, 3).iterator())
         }
         assertEquals(listOf(1, 2, 3), result.toList())
@@ -160,7 +160,7 @@ class SequenceBuilderTest {
 
     @Test
     fun testYieldAllSequence() {
-        val result = buildSequence {
+        val result = sequence {
             yieldAll(sequenceOf(1, 2, 3))
         }
         assertEquals(listOf(1, 2, 3), result.toList())
@@ -168,7 +168,7 @@ class SequenceBuilderTest {
 
     @Test
     fun testYieldAllCollection() {
-        val result = buildSequence {
+        val result = sequence {
             yieldAll(listOf(1, 2, 3))
         }
         assertEquals(listOf(1, 2, 3), result.toList())
@@ -176,7 +176,7 @@ class SequenceBuilderTest {
 
     @Test
     fun testYieldAllCollectionMixedFirst() {
-        val result = buildSequence {
+        val result = sequence {
             yield(0)
             yieldAll(listOf(1, 2, 3))
         }
@@ -185,7 +185,7 @@ class SequenceBuilderTest {
 
     @Test
     fun testYieldAllCollectionMixedLast() {
-        val result = buildSequence {
+        val result = sequence {
             yieldAll(listOf(1, 2, 3))
             yield(4)
         }
@@ -194,7 +194,7 @@ class SequenceBuilderTest {
 
     @Test
     fun testYieldAllCollectionMixedBoth() {
-        val result = buildSequence {
+        val result = sequence {
             yield(0)
             yieldAll(listOf(1, 2, 3))
             yield(4)
@@ -204,7 +204,7 @@ class SequenceBuilderTest {
 
     @Test
     fun testYieldAllCollectionMixedLong() {
-        val result = buildSequence {
+        val result = sequence {
             yield(0)
             yieldAll(listOf(1, 2, 3))
             yield(4)
@@ -219,7 +219,7 @@ class SequenceBuilderTest {
 
     @Test
     fun testYieldAllCollectionOneEmpty() {
-        val result = buildSequence<Int> {
+        val result = sequence<Int> {
             yieldAll(listOf())
         }
         assertEquals(listOf(), result.toList())
@@ -227,7 +227,7 @@ class SequenceBuilderTest {
 
     @Test
     fun testYieldAllCollectionManyEmpty() {
-        val result = buildSequence<Int> {
+        val result = sequence<Int> {
             yieldAll(listOf())
             yieldAll(listOf())
             yieldAll(listOf())
@@ -238,7 +238,7 @@ class SequenceBuilderTest {
     @Test
     fun testYieldAllSideEffects() {
         val effects = arrayListOf<Any>()
-        val result = buildSequence {
+        val result = sequence {
             effects.add("a")
             yieldAll(listOf(1, 2))
             effects.add("b")
@@ -276,7 +276,7 @@ class SequenceBuilderTest {
 
     @Test
     fun testInfiniteYieldAll() {
-        val values = buildIterator {
+        val values = iterator {
             while (true) {
                 yieldAll((1..5).map { it })
             }