improve mangle.properties (#2261)

- include dead code when `keep_quoted`
- unify `keep_quoted` & `reserved`
- make `test/run-tests.js` consistent with `minify()`

fixes #2256

test/compress/issue-1770.js

@@ -1,5 +1,7 @@
 mangle_props: {
-    mangle_props = {}
+    mangle = {
+        properties: true,
+    }
     input: {
         var obj = {
             undefined: 1,
@@ -54,10 +56,12 @@ mangle_props: {
 }
 
 numeric_literal: {
+    mangle = {
+        properties: true,
+    }
     beautify = {
         beautify: true,
     }
-    mangle_props = {}
     input: {
         var obj = {
             0: 0,
@@ -105,7 +109,9 @@ numeric_literal: {
 }
 
 identifier: {
-    mangle_props = {}
+    mangle = {
+        properties: true,
+    }
     input: {
         var obj = {
             abstract: 1,