[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/Ability.cs

@@ -6,6 +6,7 @@ namespace MyGame.Example
 {
 
 using global::System;
+using global::System.Collections.Generic;
 using global::FlatBuffers;
 
 public struct Ability : IFlatbufferObject
@@ -26,7 +27,34 @@ public struct Ability : IFlatbufferObject
     builder.PutUint(Id);
     return new Offset<MyGame.Example.Ability>(builder.Offset);
   }
+  public AbilityT UnPack() {
+    var _o = new AbilityT();
+    this.UnPackTo(_o);
+    return _o;
+  }
+  public void UnPackTo(AbilityT _o) {
+    _o.Id = this.Id;
+    _o.Distance = this.Distance;
+  }
+  public static Offset<MyGame.Example.Ability> Pack(FlatBufferBuilder builder, AbilityT _o) {
+    if (_o == null) return default(Offset<MyGame.Example.Ability>);
+    return CreateAbility(
+      builder,
+      _o.Id,
+      _o.Distance);
+  }
 };
 
+public class AbilityT
+{
+  public uint Id { get; set; }
+  public uint Distance { get; set; }
+
+  public AbilityT() {
+    this.Id = 0;
+    this.Distance = 0;
+  }
+}
+
 
 }