Implementation and tests for KT-5840 and newly created KT-7204. Now a safe call provides not-null receiver state *inside* argument list. It works also for ?. chains. #KT-5840 Fixed.

On the other hand, argument states do not propagate to successor statements for a safe call. #KT-7204 Fixed. A few additional comments.

compiler/testData/diagnostics/tests/smartCasts/safecalls/innerReceiver.kt

@@ -0,0 +1,8 @@
+fun foo(x: String): String? = x
+
+fun calc(x: String?, y: String?): Int {
+    // Smart cast because of y!! in receiver
+    x?.subSequence(y!!.subSequence(0, 1).length(), <!DEBUG_INFO_SMARTCAST!>y<!>.length())
+    // No smart cast possible
+    return y<!UNSAFE_CALL!>.<!>length()
+}