Check if `CanExecute` in `RelayCommand.Execute`

### Overview

Assume a developer wants to call `Execute` on an `ICommand` from within another view model. Sure, bad practice but it's something that could happen in a larger project. Doing so will mean that the user forgot to check if the command can actually execute at all.

I vote that we change the `RelayCommand.Execute` function to check if it can execute before performing it's action.

### API breakdown

```csharp
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public bool CanExecute(object? parameter)
{
return this.canExecute?.Invoke() != false;
}

///
public void Execute(object? parameter)
{
if (!CanExecute(parameter)
{
return;
}

this.execute();
}
```

### Usage example

Take the following example where a property is set and `NotifyCanExecuteChanged` is invoked.

```csharp
public IRelayCommand BarCommand
{
get { return this.barCommand ??= new RelayCommand(this.Bar, this.CanBar); }
}

public bool Foo
{
get { return this.foo; }
set
{
this.SetProperty(ref this.foo, value);
this.BarCommand.NotifyCanExecuteChanged();
}
}

private void CanBar()
{
return someService.CanDoSomething();
}

private void Bar()
{
// Here, we are not checking if we CanBar
// But if a user calls BarCommand.Execute() outside of the scope of this view model they may forget to call BarCommand.CanExecute()
this.someService.DoSomething();
}
```

With the new changes in place, this will be avoided. Yes, there will be cases where `CanExecute` is executed twice; but it should theoretically be a quick operation anyways.

### Breaking change?

I'm not sure

### Alternatives

We can leave the `RelayCommand` as it is and sometimes forget to call `CanExecute` where required.

### Additional context

https://stackoverflow.com/a/6985124/22134768

### Help us help you

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