Pass the type of client to GrpcClientFactoryOptions.Creator to activate

### Is your feature request related to a problem? Please describe.
Currently, [`GrpcClientFactoryOptions.Creator`](https://github.com/grpc/grpc-dotnet/blob/bf26e0377abfa86f34778ee1347565f02d90ffb5/src/Grpc.Net.ClientFactory/GrpcClientFactoryOptions.cs#L50) can implement custom client generation, but the client type is not passed to the `Creator` delegate, so we cannot generate a custom client.

The default activation process is to pass a type parameter to the `IServiceProvider` when requesting a `DefaultClientActivator`, so the client type is passed to the `DefaultClientActivator`.
https://github.com/grpc/grpc-dotnet/blob/bf26e0377abfa86f34778ee1347565f02d90ffb5/src/Grpc.Net.ClientFactory/Internal/DefaultGrpcClientFactory.cs#L50

### Describe the solution you'd like
We want to receive the client's type in a custom delegate or make ClientActivator service replaceable.

```csharp
public Func? Creator { get; set; }
```
```csharp
var c = clientFactoryOptions.Creator(callInvoker, typeof(TClient));
```

### Additional context
Our [MagicOnion](https://github.com/Cysharp/MagicOnion) project relies on Grpc.Net, but has its own implementation at the client layer.

Start in src/Grpc.Net.ClientFactory/GrpcClientFactoryOptions.cs at the Creator delegate, then read src/Grpc.Net.ClientFactory/Internal/DefaultGrpcClientFactory.cs around the DefaultClientActivator lookup. Update the custom creation path so it receives the client type as requested, and verify that the factory invokes the delegate with both the CallInvoker and typeof(TClient).

Written by the indexing model from the issue text.