FIR DFA: take all statements from ?. if result is non-null.

I.e. a?.f(b as T) != null => b is T.

This also allows to remove the copyAllInformationFrom hack by moving the
edge directly in the control flow graph.

compiler/fir/analysis-tests/testData/resolve/cfg/safeCalls.kt

@@ -1,7 +1,7 @@
 // !DUMP_CFG
 interface A {
     fun foo(): A
-    fun bar(): A
+    fun bar(x: String): A
 }
 
 interface B {
@@ -10,9 +10,15 @@ interface B {
 }
 
 fun test_1(x: A?) {
-    x?.foo()?.bar()
+    x?.foo()?.bar("")
 }
 
 fun test_2(x: B?) {
     x?.foo?.bar
 }
+
+fun test_3(x: A?, y: String?) {
+    if (x?.bar(y as String) != null) {
+        y.length
+    }
+}