Output JSON strings as natural UTF-8 text without escapes (#4710)

* Added support for the non-escaped print of utf-8 string.

* EscapeString: the first invalid symbol resets print_natural_utf8 flag to false.

* Move the test to ParseAndGenerateTextTest. Fixes.

* Removed dependence between `natural_utf8` and `allow_non_utf8` flags.

tests/unicode_test.json

@@ -1,13 +1,5 @@
 {
   "name": "unicode_test",
-  "testarrayoftables": [
-    { "name": "Цлїςσδε" },
-    { "name": "ﾌﾑｱﾑｶﾓｹﾓ" },
-    { "name": "フムヤムカモケモ" },
-    { "name": "㊀㊁㊂㊃㊄" },
-    { "name": "☳☶☲" },
-    { "name": "𡇙𝌆" }
-  ],
   "testarrayofstring": [
     "Цлїςσδε",
     "ﾌﾑｱﾑｶﾓｹﾓ",
@@ -15,5 +7,25 @@
     "㊀㊁㊂㊃㊄",
     "☳☶☲",
     "𡇙𝌆"
+  ],
+  "testarrayoftables": [
+    {
+      "name": "Цлїςσδε"
+    },
+    {
+      "name": "ﾌﾑｱﾑｶﾓｹﾓ"
+    },
+    {
+      "name": "フムヤムカモケモ"
+    },
+    {
+      "name": "㊀㊁㊂㊃㊄"
+    },
+    {
+      "name": "☳☶☲"
+    },
+    {
+      "name": "𡇙𝌆"
+    }
   ]
 }