[BE] Support until operator in back-ends

compiler/testData/codegen/box/operatorConventions/untilOperator.kt

@@ -0,0 +1,47 @@
+// WITH_STDLIB
+// !LANGUAGE: +RangeUntilOperator
+
+class ARange(_start: A, _end: A): ClosedRange<A>, Iterable<A> {
+    override val endInclusive: A = _end
+    override val start: A = _start
+    override fun iterator(): Iterator<A> = object : Iterator<A> {
+        override fun hasNext(): Boolean = hasNext
+        override fun next(): A {
+            val value = next
+            if (value == finalElement) {
+                if (!hasNext) throw kotlin.NoSuchElementException()
+                hasNext = false
+            }
+            else {
+                next += step
+            }
+            return A(value)
+        }
+    }
+
+    private val step: Int = 1
+    private val finalElement: Int = endInclusive.x
+    private var hasNext: Boolean = if (step > 0) start <= endInclusive else start >= endInclusive
+    private var next: Int = if (hasNext) start.x else finalElement
+}
+
+class A(val x: Int): Comparable<A> {
+    operator fun rangeUntil(other: A): Iterable<A> = ARange(this, A(other.x - 1))
+    operator fun rangeTo(other: A): Iterable<A> = ARange(this, other)
+    override fun compareTo(other: A): Int = this.x.compareTo(other.x)
+}
+
+fun box(): String {
+    val x = A(1)
+    val y = A(4)
+
+    var summ1 = 0
+    for (i in x..<y) {
+        summ1 += i.x
+    }
+    var summ2 = 0
+    for (i in x..y) {
+        summ2 += i.x
+    }
+    return if (summ1 == 6 && summ2 == 10) "OK" else "NOK"
+}