Preliminary declaration visitor for estimating local variable's predictability for smart casts

Predictability estimation algorithm is completely new, but backward compatibility should present.
A large set of tests. Some updated tests.
Smart casts allowed for captured variables if they are not modified in closure #KT-9051 Fixed
Also #KT-8643 Fixed
Also #KT-7976 Fixed
Correct handling of lambda arguments in functions #KT-9143 Fixed

compiler/testData/diagnostics/testsWithStdLib/smartcasts/withChangesToNull.kt

@@ -0,0 +1,10 @@
+fun foo(y: String?) {
+    var x: String? = ""
+    if (x != null) {
+        with(y?.let { x = null; it }) {
+            this<!UNSAFE_CALL!>.<!>length
+            x<!UNSAFE_CALL!>.<!>length
+        }
+        x<!UNSAFE_CALL!>.<!>length
+    }
+}