Number of vCPUs visible inside the guest.
For many GCE machine types, the number of vCPUs visible inside the guest is equal to the `compute.googleapis.com/instance/cpu/reserved_cores` metric.
For shared-core machine types, the number of guest-visible vCPUs differs from the number of reserved cores.
For example, e2-small instances have two vCPUs visible inside the guest and 0.5 fractional vCPUs reserved.
Therefore, for an e2-small instance, `compute.googleapis.com/instance/cpu/guest_visible_vcpus` has a value of 2 and `compute.googleapis.com/instance/cpu/reserved_cores` has a value of 0.5.