feature: Add Parse & TryParse to EmbedBuilder & Add ToJsonString extension (#2284)

* Add parse & tryparse to embedbuilder.

* Add tostring extension for embeds

* Modify comments

* Resolve suggestions

* Update src/Discord.Net.Rest/Extensions/StringExtensions.cs

Co-authored-by: Quin Lynch <49576606+quinchs@users.noreply.github.com>

src/Discord.Net.Rest/Extensions/StringExtensions.cs

@@ -0,0 +1,47 @@
+using Discord.Net.Converters;
+using Newtonsoft.Json;
+using System.Linq;
+using System;
+
+namespace Discord.Rest
+{
+    /// <summary>
+    ///     Responsible for formatting certain entities as Json <see langword="string"/>, to reuse later on.
+    /// </summary>
+    public static class StringExtensions
+    {
+        private static Lazy<JsonSerializerSettings> _settings = new(() =>
+        {
+            var serializer = new JsonSerializerSettings()
+            {
+                ContractResolver = new DiscordContractResolver()
+            };
+            serializer.Converters.Add(new EmbedTypeConverter());
+            return serializer;
+        });
+
+        /// <summary>
+        ///     Gets a Json formatted <see langword="string"/> from an <see cref="EmbedBuilder"/>.
+        /// </summary>
+        /// <remarks>
+        ///     See <see cref="EmbedBuilder.TryParse(string, out EmbedBuilder)"/> to parse Json back into embed.
+        /// </remarks>
+        /// <param name="builder">The builder to format as Json <see langword="string"/>.</param>
+        /// <param name="formatting">The formatting in which the Json will be returned.</param>
+        /// <returns>A Json <see langword="string"/> containing the data from the <paramref name="builder"/>.</returns>
+        public static string ToJsonString(this EmbedBuilder builder, Formatting formatting = Formatting.Indented)
+            => ToJsonString(builder.Build(), formatting);
+
+        /// <summary>
+        ///     Gets a Json formatted <see langword="string"/> from an <see cref="Embed"/>.
+        /// </summary>
+        /// <remarks>
+        ///     See <see cref="EmbedBuilder.TryParse(string, out EmbedBuilder)"/> to parse Json back into embed.
+        /// </remarks>
+        /// <param name="embed">The embed to format as Json <see langword="string"/>.</param>
+        /// <param name="formatting">The formatting in which the Json will be returned.</param>
+        /// <returns>A Json <see langword="string"/> containing the data from the <paramref name="embed"/>.</returns>
+        public static string ToJsonString(this Embed embed, Formatting formatting = Formatting.Indented)
+            => JsonConvert.SerializeObject(embed.ToModel(), formatting, _settings.Value);
+    }
+}