Add UTF32Encoding tests.dotnet\corefx#8056

CVE-2023-52389 UTF32Encoding.cpp in POCO has a Poco::UTF32Encoding integer overflow and resultant stack buffer overflow because Poco::UTF32Encoding::convert() and Poco::UTF32::query…

Fix UTF32Encoding BOM being emitted by XmlWriter when ByteOrderMark set to false.dotnet\corefx#28194

System.Text.Encoding.WebName is wrong for System.Text.UnicodeEncoding and System.Text.UTF32Encoding.dotnet/runtime/63605

@catwalkagogo BigEndianだとUTF32Encodingですねぇ…。別にEncoding.GetEncodingでも同じですけど、クラスとして存在している方が安定してアクセスできる分、いいかなと.

UTF32Encoding and XmlTransformation when ByteOrderMark is set to false still contains the mark on .NET Core 2.dotnet\corefx#26544

Simplifies UTF32Encoding/UTF8Encoding/UnicodeEncoding ctors initialization flow.dotnet\coreclr#20072

System.Text.Encoding.WebName is wrong for System.Text.UnicodeEncoding and System.Text.UTF32Encoding.dotnet/runtime/63605

CVE-2023-52389. UTF32Encoding.cpp in POCO has a Poco::UTF32Encoding integer overflow and resultant stack buffer overflow because Poco::UTF32Encoding::convert() and Poco::UTF32::queryConvert() may return a negative .