csharp: rename ExtensionMethods

Summary:
This patch will rename `ExtensionMethods` to `Extensions` that is commonly used
in csharp project.

Depends on D10972

Test Plan: meson build -Dbindings=mono,cxx -Dmono-beta=true

Reviewers: lauromoura, Jaehyun_Cho, felipealmeida

Reviewed By: Jaehyun_Cho, felipealmeida

Subscribers: cedric, #reviewers, #committers

Tags: #efl

Differential Revision: https://phab.enlightenment.org/D10913

src/bin/eolian_mono/eolian/mono/klass.hh

@@ -404,7 +404,7 @@ struct klass
         (lit("#if EFL_BETA\n")
          << "#pragma warning disable CS1591\n" // Disabling warnings as DocFx will hide these classes
          << "public static class " << name_helpers::klass_concrete_name(cls)
-         << "ExtensionMethods {\n"
+         << "Extensions {\n"
          << extension_method_stream.str()
          << "}\n"
          << "#pragma warning restore CS1591\n"

src/bindings/mono/eina_mono/eina_slice.cs

@@ -232,7 +232,9 @@ public struct RwSlice : ISliceBase, IEquatable<RwSlice>
 
 }
 
-public static class Eina_SliceUtils
+namespace Eina
+{
+public static class SliceExtensions
 {
     public static byte[] GetBytes(this Eina.ISliceBase slc)
     {
@@ -243,3 +245,4 @@ public static class Eina_SliceUtils
         return mArray;
     }
 }
+}

src/tests/efl_mono/Eina.cs

@@ -19,6 +19,7 @@ using System.Linq;
 using System.Runtime.InteropServices;
 using System.Runtime.CompilerServices;
 
+using Eina;
 using EinaTestData;
 using static EinaTestData.BaseData;
 

src/tests/efl_mono/EinaTestData.cs

@@ -18,6 +18,7 @@ using System.Linq;
 using System.Runtime.InteropServices;
 using System.Runtime.CompilerServices;
 using System.Diagnostics.Contracts;
+using Eina;
 
 namespace EinaTestData
 {

src/tests/efl_mono/StructHelpers.cs

@@ -17,6 +17,7 @@ using System;
 using System.Linq;
 using System.Runtime.InteropServices;
 
+using Eina;
 using static EinaTestData.BaseData;
 
 namespace TestSuite