Fix SeString serialization/deserialization (#840)

* chore: add SeString JSON conversion test

* fix: SeString JSON serialization

* chore: add SeString JSON deserialization test

* chore: rename tests to abstract format away

* chore: fix typos

* fix: deserializable SeStrings

* chore: add comment to test

* chore: use DeserializeConfig in Load

Dalamud.Test/Game/Text/SeStringHandling/SeStringTests.cs

@@ -0,0 +1,68 @@
+using System;
+using Dalamud.Configuration;
+using Dalamud.Game.Text.SeStringHandling;
+using Xunit;
+
+namespace Dalamud.Test.Game.Text.SeStringHandling
+{
+    public class SeStringTests
+    {
+        private class MockConfig : IPluginConfiguration, IEquatable<MockConfig>
+        {
+            public int Version { get; set; }
+            
+            public SeString Text { get; init; }
+
+            public bool Equals(MockConfig other)
+            {
+                if (ReferenceEquals(null, other)) return false;
+                if (ReferenceEquals(this, other)) return true;
+                return Version == other.Version && Equals(Text.TextValue, other.Text.TextValue);
+            }
+
+            public override bool Equals(object obj)
+            {
+                return Equals(obj as MockConfig);
+            }
+
+            public override int GetHashCode()
+            {
+                return HashCode.Combine(Text);
+            }
+
+            public static bool operator ==(MockConfig left, MockConfig right)
+            {
+                return Equals(left, right);
+            }
+
+            public static bool operator !=(MockConfig left, MockConfig right)
+            {
+                return !Equals(left, right);
+            }
+        }
+        
+        // Dalamud#779
+        [Fact]
+        public void TestConfigSerializable()
+        {
+            var builder = new SeStringBuilder();
+            var seString = builder.AddText("Some text").Build();
+            var config = new MockConfig { Text = seString };
+            PluginConfigurations.SerializeConfig(config);
+        }
+        
+        [Fact]
+        public void TestConfigDeserializable()
+        {
+            var builder = new SeStringBuilder();
+            var seString = builder.AddText("Some text").Build();
+            var config = new MockConfig { Text = seString };
+            
+            // This relies on the type information being maintained, which is why we're using these
+            // static methods instead of default serialization/deserialization.
+            var configSerialized = PluginConfigurations.SerializeConfig(config);
+            var configDeserialized = (MockConfig)PluginConfigurations.DeserializeConfig(configSerialized);
+            Assert.Equal(config, configDeserialized);
+        }
+    }
+}