Rename IceRpc.Builder => IceRpc.Extensions.DependencyInjection

[bernardnormier]

With #3117, we need 3 namespaces when using DI:

• IceRpc, useful for calls like Into<ClientConnection>
• IceRpc.Extensions.DependencyInjection, which makes our ServiceCollection extension methods visible
• IceRpc.Builder with IInvokerBuilder and IDispatcherBuilder and some extension methods for those

In #3122, Jose moved most (but not all) IInvokerBuilder and IDispatcherBuilder extension methods from IceRpc.Builder to IceRpc.Extensions.DependencyInjection. That's fine but it doesn't go far enough. We don't need this IceRpc.Builder namespace: IInvokerBuilder and IDispatcherBuilder should go into IceRpc.Extensions.DependencyInjection.

With this setup:

• DI-container agnostic DI abstractions / extension methods are in namespace IceRpc.Extensions.DependencyInjection and in assemblies IceRpc.dll, IceRpc.Logger.dll etc.
• MS DI-container-specific extension methods are in the same namespace but in assembly IceRpc.Extensions.DependencyInjection.dll

This could be slightly confusing but I think that's fine. It's all about DI.

[pepone]

Where will you put src/IceRpc/Builder/*.cs files, src/IceRpc?

[bernardnormier]

in src/IceRpc/Extensions/DependencyInjection

[pepone]

Fixed in #3122