Added HV Socket known IDs, Dial, bug fixes (#239)

* Added HV Socket known IDs, Dial, bug fixes

Added:
* Well-know Hyper-V VMIDs for parents, children, and loopback.
* VSock interop service GUID.
* `Dial()` and `DialContext()` to dial a specific Hyper-V socket at a
  known address (along with a corresponding `HvsockDialer` struct.

Bug fixes:
* Dial (and Listen) now properly initialize and set properties of their
  sockets after ConnectEx (and AcceptEx).
* The `socketError` used by `bind` was incorrect, it should be `int32(-1)`,
  not `uintptr(^0)`
* Return errors for `(*HvsockConn) SetDeadline`

Created a `sockets` package, currently only with syscalls to `Bind`,
`ConnectEx` and `GetSockName`, bypassing `syscall/windows` restrictions
on the types that can do so.

Signed-off-by: Hamza El-Saawy <hamzaelsaawy@microsoft.com>

* PR: error handling bug, rebase, unexport, naming

* comments and todos statements
* spelling
* removed dead code
* changed names to be more conventional
* unexported socket code
* made `(*HvsockDialer) Dial` take `Context`, removed `DialContext`
* added default `Dial` function
* rebased onto main
* cleaned up `Dial(` retry loop

Signed-off-by: Hamza El-Saawy <hamzaelsaawy@microsoft.com>

* PR: RawSockaddr validation, `.As(` style

Signed-off-by: Hamza El-Saawy <hamzaelsaawy@microsoft.com>

file.go

@@ -178,6 +178,8 @@ func ioCompletionProcessor(h syscall.Handle) {
 	}
 }
 
+// todo: helsaawy - create an asyncIO version that takes a context
+
 // asyncIo processes the return value from ReadFile or WriteFile, blocking until
 // the operation has actually completed.
 func (f *win32File) asyncIo(c *ioOperation, d *deadlineHandler, bytes uint32, err error) (int, error) {
@@ -221,6 +223,7 @@ func (f *win32File) asyncIo(c *ioOperation, d *deadlineHandler, bytes uint32, er
 	// runtime.KeepAlive is needed, as c is passed via native
 	// code to ioCompletionProcessor, c must remain alive
 	// until the channel read is complete.
+	// todo: (de)allocate *ioOperation via win32 heap functions, instead of needing to KeepAlive?
 	runtime.KeepAlive(c)
 	return int(r.bytes), err
 }