Theme controls do not show/hide when the checkbox is toggled #4502

Toggling the Enable Theming checkbox has no visible effect on the preference page. When the checkbox is unchecked, the Theme combo, Colors and Fonts Theme combo, and Manage Default button stay visible — they should disappear. When the checkbox is re-checked (after a restart with theming disabled), those controls never appear — the page looks exactly the same as when theming was off.

Steps to reproduce

1. (unchecked → controls stay visible)
   Open Window → Preferences → General → Appearance with theming currently enabled.
   Uncheck Enable Theming.
   Current behaviour: Theme combo, Colors and Fonts combo, and Manage Default button are still visible.
   Expected: Those controls are hidden immediately.

2. (checked → controls never appear)
   Disable theming and restart Eclipse (so theming is off on launch).
   Open Window → Preferences → General → Appearance.
   Re-check Enable Theming.
   Current behaviour: No theme controls appear — the page looks identical to the unchecked state.
   Expected: Theme combo and Colors and Fonts combo appear immediately, pre-populated with available themes.

Tested under this environment:

Eclipse SDK
Version: 2026-12 (4.42)
Build id: I20261015-2300
OS: Mac OS X, v.27.0.1, aarch64 / cocoa