macOS: Reflect platform settings for double click and key repeat intervals

The KeyboardAutoRepeatRate is unfortunately exposed in QStyleHints as
an int, so any rate below 1 event per second will not be reflected
accurately.

Pick-to: 6.2 6.4
Change-Id: I506762545a1838cf007320e73827def006f5f0c2
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>

src/plugins/platforms/cocoa/qcocoatheme.mm

@@ -453,6 +453,12 @@ QVariant QCocoaTheme::themeHint(ThemeHint hint) const
         return !NSScreen.screensHaveSeparateSpaces;
     case QPlatformTheme::ShowDirectoriesFirst:
         return false;
+    case QPlatformTheme::MouseDoubleClickInterval:
+        return NSEvent.doubleClickInterval * 1000;
+    case QPlatformTheme::KeyboardInputInterval:
+        return NSEvent.keyRepeatDelay * 1000;
+    case QPlatformTheme::KeyboardAutoRepeatRate:
+        return 1.0 / NSEvent.keyRepeatInterval;
     default:
         break;
     }