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/argument.kt

@@ -0,0 +1,6 @@
+fun calc(x: List<String>?): Int {
+    // After KT-5840 fix !! assertion should become unnecessary here
+    x?.get(x<!UNNECESSARY_NOT_NULL_ASSERTION!>!!<!>.size() - 1) 
+    // x?. or x!! above should not provide smart cast here
+    return x<!UNSAFE_CALL!>.<!>size()
+}