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/smartcastInByClause.dot

@@ -139,9 +139,7 @@ digraph smartcastInByClause_kt {
     }
     24 -> {25};
     25 -> {26};
-    26 -> {27};
-    26 -> {29} [color=red];
-    26 -> {31} [color=green];
+    26 -> {27 31};
     27 -> {28};
     28 -> {29};
     29 -> {30};