Custom context menu example (#1463)

* flutter create

* Copied in from 'contextual-menu-examples' repo

* Works again with the latest updates to the branch

* Clean up anywhere example

* Clean up other examples

* Add to CI

* Updated with release version of context menus, and added platform switcher

* Generated files

* Home icon on your original platform

* Remove web_dashboard from ci, not sure why that change was there...

* Add context_menu to beta channel, but commented out, for the future

* +x permissions on the master script, which I may have accidentally changed before?

* Actual bash comment

* dart format

* Natural default platform'

* A working test, for the email page

* Import order fix

* Test some pages

* More tests

* dart format

experimental/context_menus/windows/runner/main.cpp

@@ -0,0 +1,43 @@
+#include <flutter/dart_project.h>
+#include <flutter/flutter_view_controller.h>
+#include <windows.h>
+
+#include "flutter_window.h"
+#include "utils.h"
+
+int APIENTRY wWinMain(_In_ HINSTANCE instance, _In_opt_ HINSTANCE prev,
+                      _In_ wchar_t *command_line, _In_ int show_command) {
+  // Attach to console when present (e.g., 'flutter run') or create a
+  // new console when running with a debugger.
+  if (!::AttachConsole(ATTACH_PARENT_PROCESS) && ::IsDebuggerPresent()) {
+    CreateAndAttachConsole();
+  }
+
+  // Initialize COM, so that it is available for use in the library and/or
+  // plugins.
+  ::CoInitializeEx(nullptr, COINIT_APARTMENTTHREADED);
+
+  flutter::DartProject project(L"data");
+
+  std::vector<std::string> command_line_arguments =
+      GetCommandLineArguments();
+
+  project.set_dart_entrypoint_arguments(std::move(command_line_arguments));
+
+  FlutterWindow window(project);
+  Win32Window::Point origin(10, 10);
+  Win32Window::Size size(1280, 720);
+  if (!window.Create(L"context_menus", origin, size)) {
+    return EXIT_FAILURE;
+  }
+  window.SetQuitOnClose(true);
+
+  ::MSG msg;
+  while (::GetMessage(&msg, nullptr, 0, 0)) {
+    ::TranslateMessage(&msg);
+    ::DispatchMessage(&msg);
+  }
+
+  ::CoUninitialize();
+  return EXIT_SUCCESS;
+}