[FIR] Improve the control flow graph around try expressions

1. throw goes to catches instead of main exist block
2. return goes via finally (single level only supported atm)
3. collect non-direct return to retrieve all return expressions easier

compiler/testData/diagnostics/tests/controlFlowAnalysis/deadCode/deadCodeDifferentExamples.fir.kt

@@ -113,7 +113,7 @@ fun t7() : Int {
   catch (<!THROWABLE_TYPE_MISMATCH!>e : Any<!>) {
     2
   }
-  <!UNREACHABLE_CODE!>return 1<!> // this is OK, like in Java
+  return 1 // this is OK, like in Java
 }
 
 fun t8() : Int {
@@ -123,7 +123,7 @@ fun t8() : Int {
   }
   catch (<!THROWABLE_TYPE_MISMATCH!>e : Any<!>) {
     return 1
-    2
+    <!UNREACHABLE_CODE!>2<!>
   }
   <!UNREACHABLE_CODE!>return 1<!>
 }