Preliminary: support smart casts on variables in closures

No feature support yet
So #KT-14486 In Progress

compiler/testData/diagnostics/tests/smartCasts/varnotnull/capturedInClosureOff.kt

@@ -0,0 +1,15 @@
+// !LANGUAGE: -CapturedInClosureSmartCasts
+
+fun run(f: () -> Unit) = f()
+
+fun foo(s: String?) {
+    var x: String? = null
+    if (s != null) {
+        x = s
+    }
+    if (x != null) {
+        run {
+            <!DEBUG_INFO_SMARTCAST!>x<!>.hashCode()
+        }
+    }
+}