Fix 'infix call' diagnostic for in operation

#KT-8845 Fixed

idea/testData/checker/diagnosticsMessage/operatorCallDiagnosticsOnInOperator.kt

@@ -0,0 +1,8 @@
+fun call() {
+    val list : String? = "sdfknsdkfm"
+    "x" <error descr="[UNSAFE_OPERATOR_CALL] Operator call corresponds to a dot-qualified call 'list.contains(\"x\")' which is not allowed on a nullable receiver 'list'.">in</error> list
+
+    "x" <error descr="[UNSAFE_OPERATOR_CALL] Operator call corresponds to a dot-qualified call 'list.contains(\"x\")' which is not allowed on a nullable receiver 'list'.">!in</error> list
+}
+
+<error>operator</error> fun CharSequence.contains(<warning>other</warning>: CharSequence, <warning>ignoreCase</warning>: Boolean = false): Boolean = true