Match window border color to app theme rather than OS theme (#958)

* MacOS: match window chrome to app light/dark mode when app setting is different from OS

* match window border to app theme on Windows

ui/controller/windowtheme_windows.go

@@ -0,0 +1,57 @@
+//go:build windows
+
+package controller
+
+import (
+	"runtime"
+	"syscall"
+	"unsafe"
+
+	"fyne.io/fyne/v2"
+	"golang.org/x/sys/windows/registry"
+)
+
+var (
+	dwm    = syscall.NewLazyDLL("dwmapi.dll")
+	setAtt = dwm.NewProc("DwmSetWindowAttribute")
+)
+
+func setWindowDarkTheme(hwnd uintptr, mode int) {
+	if runtime.GOOS != "windows" {
+		return
+	}
+	arg := 0
+	switch mode {
+	case 0: /*auto*/
+		if isDark() {
+			arg = 1
+		}
+	case 1: /*dark*/
+		arg = 1
+	}
+
+	// copied from Fyne internals
+	ret, _, err := setAtt.Call(uintptr(unsafe.Pointer(hwnd)), // window handle
+		20,                            // DWMWA_USE_IMMERSIVE_DARK_MODE
+		uintptr(unsafe.Pointer(&arg)), // on or off
+		4)                             // sizeof(bool for windows))
+	if ret != 0 && ret != 0x80070057 { // err is always non-nil, we check return value (except erroneous code)
+		fyne.LogError("Failed to set dark mode", err)
+	}
+}
+
+// copied from Fyne internals
+func isDark() bool {
+	k, err := registry.OpenKey(registry.CURRENT_USER, `SOFTWARE\Microsoft\Windows\CurrentVersion\Themes\Personalize`, registry.QUERY_VALUE)
+	if err != nil { // older version of Windows will not have this key
+		return false
+	}
+	defer k.Close()
+
+	useLight, _, err := k.GetIntegerValue("AppsUseLightTheme")
+	if err != nil { // older version of Windows will not have this value
+		return false
+	}
+
+	return useLight == 0
+}