eBPF for Windows should support namespace isolation

BPF objects are by default system-wide entities that can be opened via several libbpf APIs (meaning the caller receives an fd to the object). While this is useful for the general case, there are some scenarios where BPF applications need to be able to isolate themselves from other BPF applications to ensure that their state remains consistent.

To achieve this a BPF application can switch to a designated namespace. Namespaces are identified by a GUID, with the default namespace having the zero GUID (all fields in the GUID are zero). All libbpf APIs that return fds are relative to the namespace that the application has specified.