Rearrange a few settings into System category page.

- Use activity-alias to define which activity shows up in what category.
  We choose activity-alias because it creates a reference to UI we need
  without having to define a new set of intent-filter and/or category
  keys. This reduces maintainence in the long run. We should merge
  metadata from activity-alias into targetActivity when cleaning up.

- Created new System dashboard activity that hosts all system category
  tiles dynamically, and a static tile for checking system update.

Bug: 31781480
Test: manual
Test: make RunSettingsRoboTests -j40
Change-Id: Ia2d762e3e1aebd17423a395c5e6c286dc3326492

src/com/android/settings/core/InstrumentedFragment.java

@@ -33,6 +33,10 @@ public abstract class InstrumentedFragment extends ObservablePreferenceFragment
 
     protected MetricsFeatureProvider mMetricsFeatureProvider;
 
+    // metrics placeholder value. Only use this for development.
+    protected final int PLACEHOLDER_METRIC = 10000;
+    protected final int SYSTEM_CATEGORY_FRAGMENT = PLACEHOLDER_METRIC + 1;
+
     public InstrumentedFragment() {
         // Mixin that logs visibility change for activity.
         getLifecycle().addObserver(new VisibilityLoggerMixin(getMetricsCategory()));