IMessenger.Send behaviour

### Describe the bug

**Service registration:**
`AddSingleton(WeakReferenceMessenger.Default)`

**Message registration:**
`_messenger.Register(this, static (r, m) => m.Reply(r.Action1(m)));`

**Behavour:**

_Case1:_
If `Action1` is of type `Task` and we do following:
```csharp
string response = await _messenger.Send(new());

private async Task Action1(TestAsyncMessage1 msg)
{
await Task.Delay(TimeSpan.FromSeconds(5));
Trace.WriteLine("Action1 process complete");
return "hello";
}
```
the response is of type `string` and contains the value `hello`.

_Case2:_
However, if `Action1` is of type `Task` and we do following:
```csharp
Task response = await _messenger.Send(new());

private async Task Action1(TestAsyncMessage1 msg)
{
await Task.Delay(TimeSpan.FromSeconds(5));
Trace.WriteLine("Action1 process complete");
}
```
the response is of type `Task`.

**Issue:**
In _Case1_ does the `await` actually awaits the internal task (Action1) and return the value of the task, in this case the string `hello`.
In _Case2_ does the `await` awaits that the message is sent, but not the internal task (Action1).

So if we want the same behaviour for _Case2_, where we want the internal task to be completed, we have to do something like:
```csharp
Task response = await _messenger.Send(new());
await response;
```

We are now implementation our own solution, using an extension method:
```csharp
public static class ExtensionMethods
{
public static async Task ProcessTask(this IMessenger messenger, TMessage message)
where TMessage : AsyncRequestMessage
{
var task = await messenger.Send(message);
await task;
}

public static Task ProcessTask(this IMessenger messenger)
where TMessage : AsyncRequestMessage, new()
=> messenger.ProcessTask(new TMessage());
}
```

Making it possible to do following:
```csharp
await _messenger.ProcessTask(new());
```

**Description**
Depening on the return type, we have different behavour.
Is this wanted? Would it make sense to add something like `ProcessTask` to the library to extend the functionality?

### Regression

_No response_

### Steps to reproduce

Microsoft Visual Studio Professional 2022 (64-bit) - Current
Version 17.12.4

CommunityToolkit.Mvvm
Version 8.2.2

### Expected behavior

See description of bug.

### Screenshots

_No response_

### IDE and version

VS 2022

### IDE version

Version 17.12.4

### Nuget packages

- [ ] CommunityToolkit.Common
- [ ] CommunityToolkit.Diagnostics
- [ ] CommunityToolkit.HighPerformance
- [x] CommunityToolkit.Mvvm (aka MVVM Toolkit)

### Nuget package version(s)

8.2.2

### Additional context

_No response_

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