Topology pane in extended displays list

Show an empty topology pane in the extended displays list. Even show
when no external display is connected.

This will be tweaked in a follow-up CL to include the built-in display
in the pane and the displays list.

This fixes an issue where the displays list is not shown when *no*
external displays are connected, which was not the intent of the flag.
The previous flag CL ag/30358161 only respected the flag when 1 external
display was connected.

Based on mocks at go/al-mm-figma

Bug: b/352650922
Test: reboot with zero displays attached and verify display list and pane are shown
Test: on al-13 device, make the activity fullscreen and verify the margins on left and right of pane are larger
Flag: com.android.settings.flags.display_topology_pane_in_display_list
Change-Id: If39fefe943a26c817fa6f636f21eb8aaa080adde

src/com/android/settings/connecteddevice/display/DisplayTopology.kt

@@ -0,0 +1,40 @@
+/*
+ * Copyright (C) 2024 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package com.android.settings.connecteddevice.display
+
+import com.android.settings.R
+
+import android.content.Context
+
+import androidx.preference.Preference
+
+const val PREFERENCE_KEY = "display_topology_preference"
+
+/**
+ * DisplayTopologyPreference allows the user to change the display topology
+ * when there is one or more extended display attached.
+ */
+class DisplayTopologyPreference(context : Context) : Preference(context) {
+    init {
+        layoutResource = R.layout.display_topology_preference
+
+        // Prevent highlight when hovering with mouse.
+        isSelectable = false
+
+        key = PREFERENCE_KEY
+    }
+}