Failed to enable Zone-redundant for Public IP

Symptom:
According by [azure doc](https://docs.microsoft.com/en-us/azure/virtual-network/virtual-network-public-ip-address#create-a-public-ip-address), seems “Public IP” supports “Zone-redundant” when “Sku” is “Standard”. After tried with rest api, seems it failed and threw below error message while passing “Zone-redundant” to service side. If it's a bug, could you help to fix it? Thanks.

PUT https://management.azure.com/subscriptions/xx-xx-xx-xx/resourceGroups/acctestRG-pip-tester2/providers/Microsoft.Network/publicIPAddresses/acctestpublicip-tester2

Request body:
{
"location": "westus2",
"properties": {
"publicIPAllocationMethod": "Static",
"publicIPAddressVersion": "IPv4",
"idleTimeoutInMinutes": 4
},
"sku": {
"name": "Standard"
},
"tags": {},
"zones": [
"Zone-redundant"
]
}

Response body:
network.PublicIPAddressesClient#CreateOrUpdate: Failure sending request: StatusCode=400 -- Original Error: Code="InvalidAvailabilityZone" Message="The zone(s) 'Zone-redundant' for resource 'Microsoft.Network/publicIPAddresses/acctestpublicip-tester2' is not supported. The supported zones for location 'westus2' are '1,2,3'"

Start with the Microsoft.Network publicIPAddresses PUT request and compare the documented Standard SKU zone values with the service response for westus2. Determine whether the REST API specification or the service behavior is inconsistent; done means the supported zone-redundant behavior is aligned and verified against the reported request.

Written by the indexing model from the issue text.