stage3: unify to cleanup; MIR return-defer; docs+smokes updated; LLVM(harness): finalize_phis ownership, ret.py simplified, uses-predeclare; cleanup return override green; method-postfix cleanup return WIP (PHI head)

apps/tests/try_finally_break_inner_loop.nyash

@@ -9,7 +9,7 @@ static box Main {
           if (j == 2) { break }
           j = j + 1
         }
-      } finally {
+      } cleanup {
         // inner の break に関わらず finally は 1 回実行
         fin = fin + 1
       }
@@ -19,4 +19,3 @@ static box Main {
     return fin
   }
 }
-