Integrate with ARM's WhatIf API for template validation

[rjmholt]

Although having generated ARM templates as an IR can help shed light on the functioning of PSArm features, integrating with ARM's WhatIf functionality would make this nicer to use

[JustinGrote]

FYI you can get the JSON output of the Whatif Result for parsing, you don't have to parse the formatted text output https://github.com/Azure/azure-powershell/issues/12031#issuecomment-644286209