Add bluetooth as a supported Slice

To add bluetooth as a valid slice requires adding
support for Context-only preference controller
constructors, which was already planned work.

Fixes: 67997327
Test: robotests
Change-Id: I7efd20a05d5796c3327a26b1fc535d5436d1070f

tests/robotests/src/com/android/settings/slices/FakeContextOnlyPreferenceController.java

@@ -0,0 +1,19 @@
+package com.android.settings.slices;
+
+import android.content.Context;
+
+import com.android.settings.core.BasePreferenceController;
+
+public class FakeContextOnlyPreferenceController extends BasePreferenceController {
+
+    public static final String KEY = "fakeController2";
+
+    public FakeContextOnlyPreferenceController(Context context) {
+        super(context, KEY);
+    }
+
+    @Override
+    public int getAvailabilityStatus() {
+        return AVAILABLE;
+    }
+}