**Is your feature request related to a problem? Please describe.**
Electron has an API which works on macOS for detecting when the system is in Dark Mode.
[Windows 10 also has a dark mode setting](https://www.digitaltrends.com/computing/how-to-enable-dark-mode-in-windows-10/). It would be useful if the same Electron API also worked on Windows.

**Describe the solution you'd like**
1. The `systemPreferences.isDarkMode()` method should work on Windows.
2. Ideally a way of subscribing to change events, equivalent to `systemPreferences.subscribeNotification('AppleInterfaceThemeChangedNotification', callback)`. Or perhaps the `color-changed` event (or another event) would be fired by `systemPreferences`.

**Additional context**
On Windows the state of the dark mode setting [is stored in the](https://stackoverflow.com/a/51336913/365069) `HKCU(HKLM)\Software\Microsoft\Windows\CurrentVersion\Themes\Personalize\AppsUseLightTheme` registry key.

shell/browser/api/atom_api_system_preferences.cc
#include "shell/browser/api/atom_api_system_preferences.h"
#include "native_mate/dictionary.h"
#include "shell/common/native_mate_converters/callback.h"
#include "shell/common/native_mate_converters/value_converter.h"
#include "shell/common/node_includes.h"
#include "ui/gfx/animation/animation.h"
#include "ui/gfx/color_utils.h"
namespace electron {
namespace api {
SystemPreferences::SystemPreferences(v8::Isolate* isolate) {
  Init(isolate);
#if defined(OS_WIN)
  InitializeWindow();
#endif
}
SystemPreferences::~SystemPreferences() {