[C#] support Object API (#5710)

* [C#] support Object API

* fix sign-compare

* fix indent

* add new line before for loop.

* using auto whenever possible

* reduce the amout of blank lines.

* wip: support vectors of union

* done: support unions of vectors

* set C# version to 4.0
* remove null propagation operator
* remove auto property initializer
* remove expression-bodied method
* remove pattern matching

* add Example2 to NetTest.sh

* separate JavaUsage.md and CsharpUsage.md from JavaCsharpUsage.md

* add C# Object based API notes.

* support vs2010.

* remove range based for loop.

* remove System.Linq

* fix indent

* CreateSharedString to CreateString

* check shared attribute

* snake case

tests/MyGame/Example/Stat.cs

@@ -6,6 +6,7 @@ namespace MyGame.Example
 {
 
 using global::System;
+using global::System.Collections.Generic;
 using global::FlatBuffers;
 
 public struct Stat : IFlatbufferObject
@@ -49,7 +50,39 @@ public struct Stat : IFlatbufferObject
     int o = builder.EndTable();
     return new Offset<MyGame.Example.Stat>(o);
   }
+  public StatT UnPack() {
+    var _o = new StatT();
+    this.UnPackTo(_o);
+    return _o;
+  }
+  public void UnPackTo(StatT _o) {
+    _o.Id = this.Id;
+    _o.Val = this.Val;
+    _o.Count = this.Count;
+  }
+  public static Offset<MyGame.Example.Stat> Pack(FlatBufferBuilder builder, StatT _o) {
+    if (_o == null) return default(Offset<MyGame.Example.Stat>);
+    var _id = _o.Id == null ? default(StringOffset) : builder.CreateString(_o.Id);
+    return CreateStat(
+      builder,
+      _id,
+      _o.Val,
+      _o.Count);
+  }
 };
 
+public class StatT
+{
+  public string Id { get; set; }
+  public long Val { get; set; }
+  public ushort Count { get; set; }
+
+  public StatT() {
+    this.Id = null;
+    this.Val = 0;
+    this.Count = 0;
+  }
+}
+
 
 }