memory: expose virtual totals / avail values on windows

[sni]

There are 2 more memory values i'd like to use. They are there already, just not exposed by the module yet.

• https://learn.microsoft.com/en-us/windows/win32/api/sysinfoapi/ns-sysinfoapi-memorystatusex

[shirou]

Thank you for your contribute. However, we don't want to add platform specific fields anymore. We have a v4 plan which introduces platform specific structs. We will be able to add fields on it, but not developed yet.

[sni]

that's great, thank you very much.