Update Apigen to support .NET 6

Without specifically setting net6.0 as a target framework,
it is impossible to run Apigen project on M1 Macs, because
support for M1 Macs was added in .NET 6, according to this
post in MS forums [1].

To enable support for .NET 6, we had to add a NuGet dependency.
Everything else worked out of the box.

[1] https://learn.microsoft.com/en-us/answers/questions/793925/problem-installing-with-dotnet-on-m1-macos-archite

Signed-off-by: Aitor Perez Cedres <acedres@vmware.com>

Author: Zerpet

build.sh

@@ -14,7 +14,7 @@ fi
 cd "$script_dir"
 
 dotnet restore ./RabbitMQDotNetClient.sln
-dotnet run --project ./projects/Apigen/Apigen.csproj --apiName:AMQP_0_9_1 \
+dotnet run --framework "net6.0" --project ./projects/Apigen/Apigen.csproj --apiName:AMQP_0_9_1 \
     ./projects/specs/amqp0-9-1.stripped.xml \
     ./gensrc/autogenerated-api-0-9-1.cs
 dotnet build ./RabbitMQDotNetClient.sln

projects/Apigen/Apigen.csproj

@@ -1,12 +1,16 @@
 <Project Sdk="Microsoft.NET.Sdk">
 
   <PropertyGroup>
-    <TargetFramework>netcoreapp3.1</TargetFramework>
     <OutputType>Exe</OutputType>
+    <TargetFrameworks>net6.0;netcoreapp3.1</TargetFrameworks>
   </PropertyGroup>
 
   <ItemGroup>
     <Compile Include="..\RabbitMQ.Client\client\api\AmqpTimestamp.cs;..\RabbitMQ.Client\client\api\IBasicConsumer.cs;..\RabbitMQ.Client\client\api\IBasicProperties.cs;..\RabbitMQ.Client\client\api\IContentHeader.cs;..\RabbitMQ.Client\client\api\IModel.cs;..\RabbitMQ.Client\client\api\PublicationAddress.cs;..\RabbitMQ.Client\client\api\IBasicPublishBatch.cs;..\RabbitMQ.Client\client\api\BasicGetResult.cs;..\RabbitMQ.Client\client\api\QueueDeclareOk.cs;..\RabbitMQ.Client\client\api\ShutdownEventArgs.cs;..\RabbitMQ.Client\client\api\ShutdownInitiator.cs;..\RabbitMQ.Client\client\events\BasicReturnEventArgs.cs;..\RabbitMQ.Client\client\events\BasicAckEventArgs.cs;..\RabbitMQ.Client\client\events\BasicNackEventArgs.cs;..\RabbitMQ.Client\client\events\CallbackExceptionEventArgs.cs;..\RabbitMQ.Client\client\events\ConsumerEventArgs.cs;..\RabbitMQ.Client\client\events\FlowControlEventArgs.cs;..\RabbitMQ.Client\client\impl\IFullModel.cs" />
   </ItemGroup>
 
+  <ItemGroup>
+    <PackageReference Include="System.Memory" Version="4.5.5" />
+  </ItemGroup>
+
 </Project>