Instead, CPUs will be created dynamically. We also allow a relatively
efficient mechanism for stealing and notifying when a vCPU becomes
available via unlock.
Since the number of vCPUs is no longer fixed at machine creation time,
we make the dirtySet packing more efficient. This has the pleasant side
effect of cutting out the unsafe address space code.
PiperOrigin-RevId: 201266691
Change-Id: I275c73525a4f38e3714b9ac0fd88731c26adfe66