Support launching home activity on secondary display

- Add a new flag indicating that the display should show
  system decorations, such as status bar, nav bar, home and IME.
- Automatically launches home activity on secondary display
  if the display support system decorations and home
  activity has multiple instances supports.
- Remove ActivityStackSupervisor#mHomeStack and move several
  home stack related methods to ActivityDisplay.

Bug: 111363427
Test: atest ActivityManagerMultiDisplayTests
      atest com.android.server.am
      Manual test on virtual display and chromecast

Change-Id: I48fe245ad12965a19a6768f5dbb4e974ce94b01a

core/java/android/hardware/display/DisplayManager.java

@@ -297,6 +297,15 @@ public final class DisplayManager {
      */
     public static final int VIRTUAL_DISPLAY_FLAG_DESTROY_CONTENT_ON_REMOVAL = 1 << 8;
 
+    /**
+     * Virtual display flag: Indicates that the display should support system decorations. Virtual
+     * displays without this flag shouldn't show home, IME or any other system decorations.
+     *
+     * @see #createVirtualDisplay
+     * @hide
+     */
+    public static final int VIRTUAL_DISPLAY_FLAG_SHOULD_SHOW_SYSTEM_DECORATIONS = 1 << 9;
+
     /** @hide */
     public DisplayManager(Context context) {
         mContext = context;

core/java/android/view/Display.java

@@ -220,6 +220,18 @@ public final class Display {
      */
     public static final int FLAG_CAN_SHOW_WITH_INSECURE_KEYGUARD = 1 << 5;
 
+    /**
+     * Display flag: Indicates that the display should show system decorations.
+     * <p>
+     * This flag identifies secondary displays that should show system decorations, such as status
+     * bar, navigation bar, home activity or IME.
+     * </p>
+     *
+     * @see #supportsSystemDecorations
+     * @hide
+     */
+    public static final int FLAG_SHOULD_SHOW_SYSTEM_DECORATIONS = 1 << 6;
+
     /**
      * Display flag: Indicates that the contents of the display should not be scaled
      * to fit the physical screen dimensions.  Used for development only to emulate
@@ -873,6 +885,16 @@ public final class Display {
         return mDisplayInfo.removeMode;
     }
 
+    /**
+     * Returns whether this display should support showing system decorations.
+     *
+     * @see #FLAG_SHOULD_SHOW_SYSTEM_DECORATIONS
+     * @hide
+     */
+    public boolean supportsSystemDecorations() {
+        return (mDisplayInfo.flags & FLAG_SHOULD_SHOW_SYSTEM_DECORATIONS) != 0;
+    }
+
     /**
      * Returns the display's HDR capabilities.
      *