update csharp template to support implementations on oneOf

Author: HugoMario

src/main/resources/handlebars/csharp/interface.mustache

@@ -0,0 +1,12 @@
+/// <summary>
+/// {{#description}}{{.}}{{/description}}{{^description}}{{classname}}{{/description}}
+/// </summary>
+public interface {{{classname}}}
+{
+
+{{#vendorExtensions}}
+{{#x-discriminator-type-getter}}
+    {{x-discriminator-type}} {{x-discriminator-type-getter}}();
+{{/x-discriminator-type-getter}}
+{{/vendorExtensions}}
+}

src/main/resources/handlebars/csharp/model.mustache

@@ -1,4 +1,5 @@
 {{>partial_header}}
+{{^x-is-composed-model}}
 using System;
 using System.Linq;
 using System.IO;
@@ -27,12 +28,17 @@ using System.ComponentModel;
 using System.ComponentModel.DataAnnotations;
 {{/netStandard}}
 using SwaggerDateConverter = {{packageName}}.Client.SwaggerDateConverter;
-
+{{/x-is-composed-model}}
 {{#models}}
 {{#model}}
 namespace {{packageName}}.{{modelPackage}}
 {
+{{#isComposedModel}}
+    {{>interface}}
+{{/isComposedModel}}
+{{^isComposedModel}}
 {{#isEnum}}{{>modelEnum}}{{/isEnum}}{{^isEnum}}{{>modelGeneric}}{{/isEnum}}
+{{/isComposedModel}}
 {{/model}}
 {{/models}}
 }

src/main/resources/handlebars/csharp/modelGeneric.mustache

@@ -9,7 +9,7 @@
     {{#generatePropertyChanged}}
     [ImplementPropertyChanged]
     {{/generatePropertyChanged}}
-    {{>visibility}} partial class {{classname}} : {{#parent}}{{{parent}}}, {{/parent}} IEquatable<{{classname}}>{{^netStandard}}{{#validatable}}, IValidatableObject{{/validatable}}{{/netStandard}}
+    {{>visibility}} partial class {{classname}} : {{#parent}}{{{parent}}}, {{/parent}} IEquatable<{{classname}}>{{^netStandard}}{{#validatable}}, IValidatableObject{{/validatable}}{{/netStandard}}{{#interfaceModels}}{{#@first}}, {{/@first}}{{classname}}{{^@last}}, {{/@last}}{{#@last}} {{/@last}}{{/interfaceModels}}
     {
         {{#vars}}
         {{#items.isEnum}}