Fix 64-bit numeric enum values in typescript (#7135)

* Fix 64-bit default numeric enum values in typescript

If you had a default value that wasn't a valid enum value (e.g., a zero
if you used a bit_flag setting, like you get with AdvancedFeatures
in reflection.fbs), we weren't using BigInt.

* Run generate_code.py

* [DART] Handle deprecated fields & invalid enum defaults

* Update .NET test

tests/MyGame/Example/LongEnum.cs

@@ -0,0 +1,18 @@
+// <auto-generated>
+//  automatically generated by the FlatBuffers compiler, do not modify
+// </auto-generated>
+
+namespace MyGame.Example
+{
+
+[Newtonsoft.Json.JsonConverter(typeof(Newtonsoft.Json.Converters.StringEnumConverter))]
+[System.FlagsAttribute]
+public enum LongEnum : ulong
+{
+  LongOne = 2,
+  LongTwo = 4,
+  LongBig = 1099511627776,
+};
+
+
+}