Fix typeconverter culture handling

I guess tests are actually useful?

Author: Morilli

src/BizHawk.Emulation.Common/Json/TypeConverterJsonAdapter.cs

@@ -1,4 +1,5 @@
-using System.ComponentModel;
+using System.ComponentModel;
+using System.Globalization;
 using System.Linq;
 using System.Reflection;
 using System.Text.Json;
@@ -17,14 +18,14 @@ public class TypeConverterJsonAdapter<T> : JsonConverter<T>
 		public override T Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
 		{
 			var converter = TypeDescriptor.GetConverter(typeToConvert);
-			return (T)converter.ConvertFromString(reader.GetString())!;
+			return (T)converter.ConvertFromString(null!, CultureInfo.InvariantCulture, reader.GetString())!;
 		}
 
 		/// <inheritdoc/>
 		public override void Write(Utf8JsonWriter writer, T objectToWrite, JsonSerializerOptions options)
 		{
 			var converter = TypeDescriptor.GetConverter(objectToWrite!);
-			writer.WriteStringValue(converter.ConvertToString(objectToWrite!));
+			writer.WriteStringValue(converter.ConvertToString(null!, CultureInfo.InvariantCulture, objectToWrite!));
 		}
 
 		/// <inheritdoc/>

src/BizHawk.Tests/Client.Common/config/SerializationStabilityTests.cs

@@ -126,7 +126,7 @@ public void TestSerializationTypeConverter()
 		{
 			var color = Color.FromArgb(200, 255, 13, 42);
 			string serialized = JsonSerializer.Serialize(color, ConfigService.SerializerOptions);
-			Assert.AreEqual("\"200; 255; 13; 42\"", serialized);
+			Assert.AreEqual("\"200, 255, 13, 42\"", serialized);
 
 			var newColor = JsonSerializer.Deserialize<Color>(serialized, ConfigService.SerializerOptions);
 			Assert.AreEqual(color, newColor);