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/smartcasts/controlStructures/elvis.dot

@@ -62,9 +62,7 @@ digraph elvis_kt {
     5 -> {6};
     6 -> {7};
     7 -> {8};
-    8 -> {9};
-    8 -> {11} [color=red];
-    8 -> {13} [color=green];
+    8 -> {9 13};
     9 -> {10};
     10 -> {11};
     11 -> {12};