Add ProcessInfo2 call

[simonswine]

This implements the ProcessInfo2 call, to figure out more information about the process and runtime

[kolesnikovae]

Looks good! There's one minor issue with the parser error check – please take a look

[kolesnikovae]

We need to check the parser error with p.Err() in the end

nit:

It looks like the buffer size is known in advance, probably we should pre-alloc it. Also, for small payloads of known size io.ReadAtLeast might be a better alternative to io.Copy. Provided that we will be calling ProcessInfo2 relatively frequently, this micro-optimisation might make sense. Also, we could parse all fields with parser, like:

	md := Metadata{p: &Parser{Buffer: blob.Payload}}
	md.p.Read(&md.Header.MetaDataID)
	md.Header.ProviderName = md.p.UTF16NTS()
	md.p.Read(&md.Header.EventID)
	md.Header.EventName = md.p.UTF16NTS()
	md.p.Read(&md.Header.Keywords)
	md.p.Read(&md.Header.Version)
	md.p.Read(&md.Header.Level)

There's probably a bug in the UTF16NTS() function, as it should be called once per a string:

• It looks like the fallback path (decodeUTF16NTS) only works as intended if the very first char is a non-ASCII one
• the function is quite wasteful: we probably should reuse bytes buffer / use strings.Buidler

[kolesnikovae]

It would be great if we could get the error code when CommandID is 0xFF

In readResponse we have quite weak check, and a TODO note – I'd fix this:

func verifyResponseHeader(h Header) error {
	if h.CommandSet != CommandSetServer {
		return  fmt.Errorf("%w: received response with unknown command set %#x", ErrDiagnosticServer, h.CommandSet)
	}
	switch h.CommandID {
	default:
		return fmt.Errorf("%w: received response with unknown command ID %#x", ErrDiagnosticServer, h.CommandID)
	case 0x00:
		return nil
	case 0xFF:
		var er ErrorResponse
		if err := binary.Read(r, binary.LittleEndian, &er); err != nil {
			return err
		}
		return fmt.Errorf("%w: error code %#x", ErrDiagnosticServer, er.Code)
	}
}