Return back-up slices for unavailable settings

When an inline slice is requested, and the setting is unavailable,
we should present more useful information to the user. This CL handles:
- Unsupported: return intent slice to Settings home page
- Disabled for user: intent to the setting page
- Unknown reason: intent to setting page
- Disabled dependency: Create intent-based Slice rather
than the requested inline slice.

Bug: 71640747
Test: robotests
Change-Id: I9c1a0ee36119d4f9f3b205e0824c251f4356db55

src/com/android/settings/slices/SettingsSliceProvider.java

@@ -90,6 +90,12 @@ public class SettingsSliceProvider extends SliceProvider {
      */
     public static final String EXTRA_SLICE_KEY = "com.android.settings.slice.extra.key";
 
+    /**
+     * Boolean extra to indicate if the Slice is platform-defined.
+     */
+    public static final String EXTRA_SLICE_PLATFORM_DEFINED =
+            "com.android.settings.slice.extra.platform";
+
     // TODO -- Associate slice URI with search result instead of separate hardcoded thing
 
     @VisibleForTesting