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/falseExtension.kt

@@ -0,0 +1,7 @@
+fun String.foo(y: Int) = y
+
+fun calc(x: List<String>?): Int {
+    "abc".foo(x!!.size())
+    // Here we should have smart cast because of x!!, despite of KT-7204 fixed
+    return <!DEBUG_INFO_SMARTCAST!>x<!>.size()
+}