Move changes from dfb379d under new language feature (#KT-28672)

Changes from that commit are breaking, and should be pass throw LC

compiler/testData/diagnostics/testsWithStdLib/contracts/smartcasts/extensionReceiver.kt

@@ -20,7 +20,7 @@ fun smartcastOnReceiver(s: String?) {
             <!UNSAFE_CALL!>length<!>
         }
         else {
-            <!DEBUG_INFO_IMPLICIT_RECEIVER_SMARTCAST!>length<!>
+            <!UNSAFE_CALL!>length<!>
         }
     }
 }

compiler/testData/diagnostics/testsWithStdLib/contracts/smartcasts/extensionReceiver_after.kt

@@ -0,0 +1,38 @@
+// !LANGUAGE: +AllowContractsForCustomFunctions +UseReturnsEffect +ContractsOnCallsWithImplicitReceiver
+// !USE_EXPERIMENTAL: kotlin.contracts.ExperimentalContracts
+// !DIAGNOSTICS: -INVISIBLE_REFERENCE -INVISIBLE_MEMBER
+//
+// ISSUE: KT-28672
+
+import kotlin.contracts.*
+
+fun CharSequence?.isNullOrEmpty(): Boolean {
+    contract {
+        returns(false) implies (this@isNullOrEmpty != null)
+    }
+
+    return this == null || <!DEBUG_INFO_SMARTCAST!>this<!>.length == 0
+}
+
+fun smartcastOnReceiver(s: String?) {
+    with(s) {
+        if (isNullOrEmpty()) {
+            <!UNSAFE_CALL!>length<!>
+        }
+        else {
+            <!DEBUG_INFO_IMPLICIT_RECEIVER_SMARTCAST!>length<!>
+        }
+    }
+}
+
+fun mixedReceiver(s: String?) {
+    if (!s.isNullOrEmpty()) {
+        with(<!DEBUG_INFO_SMARTCAST!>s<!>) {
+            length
+        }
+    } else {
+        with(s) {
+            <!UNSAFE_CALL!>length<!>
+        }
+    }
+}

compiler/testData/diagnostics/testsWithStdLib/contracts/smartcasts/extensionReceiver_after.txt

@@ -0,0 +1,6 @@
+package
+
+public fun mixedReceiver(/*0*/ s: kotlin.String?): kotlin.Unit
+public fun smartcastOnReceiver(/*0*/ s: kotlin.String?): kotlin.Unit
+public fun kotlin.CharSequence?.isNullOrEmpty(): kotlin.Boolean
+    Returns(FALSE) -> <this> != null