Add contract to checkNotNull overload without message

^KT-25303 Fixed

compiler/testData/diagnostics/testsWithStdLib/contracts/fromStdlib/check.kt

@@ -22,7 +22,12 @@ fun testCheckWithFailingMessage(x: Any?) {
     <!DEBUG_INFO_SMARTCAST!>x<!>.length
 }
 
-fun tesCheckNotNullWithMessage(x: Int?) {
+fun testCheckNotNullWithMessage(x: Int?) {
-    checkNotNull(x) { "x is null!"}
+    checkNotNull(x) { "x is null!" }
+    <!DEBUG_INFO_SMARTCAST!>x<!>.inc()
+}
+
+fun testCheckNotNull(x: Int?) {
+    checkNotNull(x)
     <!DEBUG_INFO_SMARTCAST!>x<!>.inc()
 }

compiler/testData/diagnostics/testsWithStdLib/contracts/fromStdlib/check.txt

@@ -1,6 +1,7 @@
 package
 
-public fun tesCheckNotNullWithMessage(/*0*/ x: kotlin.Int?): kotlin.Unit
+public fun testCheckNotNull(/*0*/ x: kotlin.Int?): kotlin.Unit
+public fun testCheckNotNullWithMessage(/*0*/ x: kotlin.Int?): kotlin.Unit
 public fun testCheckSmartcast(/*0*/ x: kotlin.Any?): kotlin.Unit
 public fun testCheckUnreachableCode(): kotlin.Unit
 public fun testCheckWithFailingMessage(/*0*/ x: kotlin.Any?): kotlin.Unit

libraries/stdlib/src/kotlin/util/Preconditions.kt

@@ -106,7 +106,12 @@ public inline fun check(value: Boolean, lazyMessage: () -> Any): Unit {
  * @sample samples.misc.Preconditions.failCheckWithLazyMessage
  */
 @kotlin.internal.InlineOnly
-public inline fun <T : Any> checkNotNull(value: T?): T = checkNotNull(value) { "Required value was null." }
+public inline fun <T : Any> checkNotNull(value: T?): T {
+    contract {
+        returns() implies (value != null)
+    }
+    return checkNotNull(value) { "Required value was null." }
+}
 
 /**
  * Throws an [IllegalStateException] with the result of calling [lazyMessage]  if the [value] is null. Otherwise