Make Array.indices extension property, move to stdlib

This is not something that needs to be intrinsified. Note that compiler
optimizations are still possible and the fact whether 'indices' is a member or
an extension is irrelevant to the optimizer

compiler/testData/codegen/boxWithStdlib/arrays/indices.kt

@@ -0,0 +1,9 @@
+fun box(): String {
+    val a = Array<Int>(5, {it})
+    val x = a.indices.iterator()
+    while (x.hasNext()) {
+        val i = x.next()
+        if (a[i] != i) return "Fail $i ${a[i]}"
+    }
+    return "OK"
+}

compiler/testData/codegen/boxWithStdlib/arrays/indicesChar.kt

@@ -0,0 +1,9 @@
+fun box(): String {
+    val a = CharArray(5)
+    val x = a.indices.iterator()
+    while (x.hasNext()) {
+        val i = x.next()
+        if (a[i] != 0.toChar()) return "Fail $i ${a[i]}"
+    }
+    return "OK"
+}

compiler/testData/codegen/boxWithStdlib/ranges/forIntRange.kt

@@ -0,0 +1,13 @@
+fun box() : String {
+    val a = arrayOfNulls<String>(3)
+    a[0] = "a"
+    a[1] = "b"
+    a[2] = "c"
+
+    var result = 0
+    for(i in a.indices) {
+      result += i
+    }
+    if (result != 3) return "FAIL"
+    return "OK"
+}

compiler/testData/codegen/boxWithStdlib/regressions/kt998.kt

@@ -0,0 +1,34 @@
+fun findPairless(a : IntArray) : Int {
+  @loop for (i in a.indices) {
+    for (j in a.indices) {
+      if (i != j && a[i] == a[j]) continue@loop
+    }
+    return a[i]
+  }
+  return -1
+}
+
+fun hasDuplicates(a : IntArray) : Boolean {
+  var duplicate = false
+  @loop for (i in a.indices) {
+    for (j in a.indices) {
+      if (i != j && a[i] == a[j]) {
+        duplicate = true
+        break@loop
+      }
+    }
+  }
+  return duplicate
+}
+
+fun box() : String {
+    val a = IntArray(5)
+    a[0] = 0
+    a[1] = 0
+    a[2] = 1
+    a[3] = 1
+    a[4] = 5
+    if(findPairless(a) != 5) return "fail"
+    return if(hasDuplicates(a))  "OK" else "fail"
+
+}