Add VersionString
Add VersionString

We conditionally format version with VersionPrerelease in a number of
places. Add a package-level function where we can unify the version
format. Replace most of version formatting in terraform, but leave th
few instances set from the top-level package to make sure we don't break
anything before release.

sebastus/terraform-provider-azurerm,abhijeetgaiha/terraform-provider-azurerm,abhijeetgaiha/terraform-provider-azurerm,thiagocaiubi/terraform-provider-azurerm,sebastus/terraform-provider-azurerm,thiagocaiubi/terraform-provider-azurerm,sebastus/terraform-provider-azurerm,abhijeetgaiha/terraform-provider-azurerm,thiagocaiubi/terraform-provider-azurerm