macos: add padded-notch option for macos-non-native-fullscreen

Finishes #378
Supercedes #4159

This adds a new enum value for `macos-non-native-fullscreen`:
`padded-notch`. This value will add padding to the top of the window to
account for the notch on applicable devices while still hiding the
menu.

This value is preferred over "visible-menu" by some people because for
screens without a notch, the window will take up the full height.

The plan in the future is that we may color the padded area when a notch
is present. In this commit it appears as transparent.

macos/Sources/Ghostty/FullscreenMode+Extension.swift

@@ -13,6 +13,9 @@ extension FullscreenMode {
         case GHOSTTY_FULLSCREEN_NON_NATIVE_VISIBLE_MENU:
                 .nonNativeVisibleMenu
 
+        case GHOSTTY_FULLSCREEN_NON_NATIVE_PADDED_NOTCH:
+                .nonNativePaddedNotch
+
         default:
             nil
         }