Migrated the Person class to its own file

Because we are expecting usage of Person across
other surfaces, we migrate the class out
of he Notification class which is already incredibly
huge.

Test: Migrated existing cts test
Change-Id: Ia487ae7965b5ca2b016245d21faa63e3b4628344
Fixes: 75980526
diff --git a/core/java/com/android/internal/widget/MessagingGroup.java b/core/java/com/android/internal/widget/MessagingGroup.java
index f73b607..07d78fe 100644
--- a/core/java/com/android/internal/widget/MessagingGroup.java
+++ b/core/java/com/android/internal/widget/MessagingGroup.java
@@ -20,7 +20,7 @@
 import android.annotation.NonNull;
 import android.annotation.Nullable;
 import android.annotation.StyleRes;
-import android.app.Notification;
+import android.app.Person;
 import android.content.Context;
 import android.graphics.Point;
 import android.graphics.Rect;
@@ -63,7 +63,7 @@
     private boolean mFirstLayout;
     private boolean mIsHidingAnimated;
     private boolean mNeedsGeneratedAvatar;
-    private Notification.Person mSender;
+    private Person mSender;
     private boolean mImagesAtEnd;
     private ViewGroup mImageContainer;
     private MessagingImageMessage mIsolatedMessage;
@@ -126,7 +126,7 @@
         return position;
     }
 
-    public void setSender(Notification.Person sender, CharSequence nameOverride) {
+    public void setSender(Person sender, CharSequence nameOverride) {
         mSender = sender;
         if (nameOverride == null) {
             nameOverride = sender.getName();
@@ -466,7 +466,7 @@
         return mNeedsGeneratedAvatar;
     }
 
-    public Notification.Person getSender() {
+    public Person getSender() {
         return mSender;
     }