Makes Caption Language searchable only if captions are enabled.

Fix: 354785578
Flag: com.android.settings.accessibility.fix_a11y_settings_search
Test: atest CaptioningMoreOptionsFragmentTest
Test: adb shell pm clear com.google.android.settings.intelligence;
      disable captioning;
      search Settings for 'language', observe caption language missing
      enable captioning;
      search Settings for 'language', observe caption language present
Change-Id: I015d2c77fbd3f7b8fe713bafb3a49a86160ca958