Rename SuccessOrFailure to Result and hide Failure from ABI

* The members of Result are isSuccess, isFailure, exceptionOrNull, getOrNull
* The rest of API is implemented via inline-only extensions
* There are two internal functions to hide detailed mechanics of an internal
  Result.Failure class: createFailure and throwOnFailure
* Result.toString is explicit: either Success(v) or Failure(x)

See KT-26538

compiler/testData/codegen/bytecodeText/coroutines/doNotReassignContinuation.kt

@@ -4,7 +4,7 @@
 import kotlin.coroutines.*
 import kotlin.coroutines.intrinsics.*
 suspend fun suspendHere(): String = suspendCoroutineUninterceptedOrReturn { x ->
-    x.resumeWith(SuccessOrFailure.success("OK"))
+    x.resumeWith(Result.success("OK"))
 }
 
 suspend fun suspendThere(param: Int, param2: String, param3: Long): String {

compiler/testData/codegen/bytecodeText/inlineClasses/resultApiDoesntUseBox.kt

@@ -0,0 +1,37 @@
+// WITH_COROUTINES
+// FILE: test.kt
+fun test() {
+    val result = Result.success("yes!")
+    val failure = Result.failure<String>(Exception())
+
+    if (result.isSuccess) println("success")
+    if (result.isFailure) println("failure")
+    println(result.getOrThrow())
+    println(failure.getOrNull())
+    println(failure.exceptionOrNull())
+
+    val other = Result.success("nope")
+    if (result == other) println("==")
+    if (result != other) println("!=")
+    if (result.equals(other)) println("equals")
+    if (!result.equals(other)) println("!equals")
+
+    println(result.hashCode())
+    println(result.toString())
+    println("$result")
+
+    val ans1 = runCatching { 42 }
+    println(ans1)
+
+    val ans2 = 42.runCatching { this }
+    println(ans2)
+
+    println(result.getOrElse { "oops" })
+    println(result.getOrDefault("oops"))
+}
+
+// @TestKt.class:
+// 0 INVOKESTATIC Result.box-impl
+// 0 INVOKESTATIC Result.unbox-impl
+// 0 Result\$Failure
+// 53 Result

compiler/testData/codegen/bytecodeText/inlineClasses/successOrFailureApiDoesntUseErasedClass.kt

@@ -1,36 +0,0 @@
-// WITH_COROUTINES
-// FILE: test.kt
-fun testSoF() {
-    val sof = SuccessOrFailure.success("yes!")
-    val failure = SuccessOrFailure.failure<String>(Exception())
-
-    if (sof.isSuccess) println("success")
-    if (sof.isFailure) println("failure")
-    println(sof.getOrThrow())
-    println(failure.getOrNull())
-    println(failure.exceptionOrNull())
-
-    val other = SuccessOrFailure.success("nope")
-    if (sof == other) println("==")
-    if (sof != other) println("!=")
-    if (sof.equals(other)) println("equals")
-    if (!sof.equals(other)) println("!equals")
-
-    println(sof.hashCode())
-    println(sof.toString())
-    println("$sof")
-
-    val ans1 = runCatching { 42 }
-    println(ans1)
-
-    val ans2 = 42.runCatching { this }
-    println(ans2)
-
-    println(sof.getOrElse { "oops" })
-    println(sof.getOrDefault("oops"))
-}
-
-// @TestKt.class:
-// 0 SuccessOrFailure\$Erased
-// 0 SuccessOrFailure\-Erased
-// 58 SuccessOrFailure