[Doc]: Get-AzDeploymentWhatIfResult: Wrong default values in Get-Help output

### Description

The documentation for the `Get-AzDeploymentWhatIfResult` returns unsatisfying details about its parameters.

For instance, calling `Get-Help 'Get-AzDeploymentWhatIfResult' -Parameter 'ResultFormat'` [returns](https://docs.microsoft.com/en-us/powershell/module/az.resources/get-azdeploymentwhatifresult?view=azps-8.2.0#parameters):

```
Default value None
```

… which isn't true for an enumeration parameter. And `None` isn't helpful, too.

A documentation should give full explanation of what to expect from running a Cmdlet. Then, things can be coded without first testing each and every Cmdlet per se.

Please, get clear on default values of Azure PowerShell Cmdlets. This is true for each of them.