feature: Implement Dispose for types which have disposable data (#1171)

* Initial set of dispose implementations

Not handled yet:
- Discord.Net.Websocket/Entities/SocketGuild
- Discord.Net.Tests

* Refactor DiscordSocketClient init into ctor

This way we remove an IDisposableAnalyzer warning for not disposing
the client when we set the client variable.

* Dispose of clients when disposing sharded client

* Finish implementing IDisposable where appropriate

I opted to use NoWarn in the Tests project as it wasn't really necessary
considering that our tests only run once

* Tweak samples after feedback

src/Discord.Net.Core/Discord.Net.Core.csproj

@@ -12,4 +12,7 @@
     <PackageReference Include="System.Collections.Immutable" Version="1.3.1" />
     <PackageReference Include="System.Interactive.Async" Version="3.1.1" />
   </ItemGroup>
+  <ItemGroup Condition=" '$(Configuration)' != 'Release' ">
+    <PackageReference Include="IDisposableAnalyzers" Version="2.0.3.3" />
+  </ItemGroup>
 </Project>

src/Discord.Net.Core/Entities/Image.cs

@@ -1,15 +1,21 @@
+using System;
 using System.IO;
+
 namespace Discord
 {
     /// <summary>
     ///     An image that will be uploaded to Discord.
     /// </summary>
-    public struct Image
+    public struct Image : IDisposable
     {
+        private bool _isDisposed;
+
         /// <summary>
         ///     Gets the stream to be uploaded to Discord.
         /// </summary>
+#pragma warning disable IDISP008
         public Stream Stream { get; }
+#pragma warning restore IDISP008
         /// <summary>
         ///     Create the image with a <see cref="System.IO.Stream"/>.
         /// </summary>
@@ -19,6 +25,7 @@ namespace Discord
         /// </param>
         public Image(Stream stream)
         {
+            _isDisposed = false;
             Stream = stream;
         }
 
@@ -45,15 +52,28 @@ namespace Discord
         /// The specified <paramref name="path"/> is invalid, (for example, it is on an unmapped drive).
         /// </exception>
         /// <exception cref="System.UnauthorizedAccessException">
-        /// <paramref name="path" /> specified a directory.-or- The caller does not have the required permission. 
+        /// <paramref name="path" /> specified a directory.-or- The caller does not have the required permission.
         /// </exception>
-        /// <exception cref="FileNotFoundException">The file specified in <paramref name="path" /> was not found. 
+        /// <exception cref="FileNotFoundException">The file specified in <paramref name="path" /> was not found.
         /// </exception>
         /// <exception cref="IOException">An I/O error occurred while opening the file. </exception>
         public Image(string path)
         {
+            _isDisposed = false;
             Stream = File.OpenRead(path);
         }
 
+        /// <inheritdoc/>
+        public void Dispose()
+        {
+            if (!_isDisposed)
+            {
+#pragma warning disable IDISP007
+                Stream?.Dispose();
+#pragma warning restore IDISP007
+
+                _isDisposed = true;
+            }
+        }
     }
 }

src/Discord.Net.Core/Net/Rest/IRestClient.cs

@@ -1,3 +1,4 @@
+using System;
 using System.Collections.Generic;
 using System.Threading;
 using System.Threading.Tasks;
@@ -7,7 +8,7 @@ namespace Discord.Net.Rest
     /// <summary>
     ///     Represents a generic REST-based client.
     /// </summary>
-    public interface IRestClient
+    public interface IRestClient : IDisposable
     {
         /// <summary>
         ///     Sets the HTTP header of this client for all requests.

src/Discord.Net.Core/Net/Udp/IUdpSocket.cs

@@ -4,7 +4,7 @@ using System.Threading.Tasks;
 
 namespace Discord.Net.Udp
 {
-    public interface IUdpSocket
+    public interface IUdpSocket : IDisposable
     {
         event Func<byte[], int, int, Task> ReceivedDatagram;
 

src/Discord.Net.Core/Net/WebSockets/IWebSocketClient.cs

@@ -4,7 +4,7 @@ using System.Threading.Tasks;
 
 namespace Discord.Net.WebSockets
 {
-    public interface IWebSocketClient
+    public interface IWebSocketClient : IDisposable
     {
         event Func<byte[], int, int, Task> BinaryMessage;
         event Func<string, Task> TextMessage;