Static value analysis

[stan-sz]

Bicep version
Bicep CLI version 0.2.328 (a13b032)

Describe the bug
A string value could be determined at build-time to avoid the warning.

To Reproduce

var redis_size = 'C2'
resource redis 'Microsoft.Cache/Redis@2019-07-01' = {
    name: 'redis'
    location: 'westus'
    properties: {
        sku: {
            name: 'Standard'
            family: first(redis_size)
            capacity: int(last(redis_size))
        }
    }
}

Building the file above yields a warning:

Warning BCP036: The property "family" expected a value of type "'C' | 'P'" but the provided value is of type "string".

Possibly related to #795

[alex-frankel]

Closing as dup of #444