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/receiverAndChain.kt

@@ -0,0 +1,8 @@
+fun foo(x: String): String? = x
+
+fun calc(x: String?): Int {
+    // Smart cast because of x!! in receiver
+    foo(x!!)?.subSequence(0, <!DEBUG_INFO_SMARTCAST!>x<!>.length())?.length()
+    // Smart cast because of x!! in receiver
+    return <!DEBUG_INFO_SMARTCAST!>x<!>.length()    
+}