AOSP/Messaging - Update language to comply with Android's inclusive language guidance.

See https://source.android.com/setup/contribute/respectful-code for reference

BUG=161896447

Test: make and make messagingtests
Change-Id: I01c520f1d5e9eab8dbb25b08d133ae34bd301093

src/com/android/messaging/mmslib/pdu/PduPersister.java

@@ -1440,7 +1440,7 @@ public class PduPersister {
 
         // Save parts first to avoid inconsistent message is loaded
         // while saving the parts.
-        final long dummyId = System.currentTimeMillis(); // Dummy ID of the msg.
+        final long placeholderId = System.currentTimeMillis(); // Placeholder ID of the msg.
 
         // Figure out if this PDU is a text-only message
         boolean textOnly = true;
@@ -1463,7 +1463,7 @@ public class PduPersister {
                 }
                 for (int i = 0; i < partsNum; i++) {
                     final PduPart part = body.getPart(i);
-                    persistPart(part, dummyId, preOpenedFiles);
+                    persistPart(part, placeholderId, preOpenedFiles);
 
                     // If we've got anything besides text/plain or SMIL part, then we've got
                     // an mms message with some other type of attachment.
@@ -1501,14 +1501,14 @@ public class PduPersister {
                 throw new MmsException("persist() failed: return null.");
             }
             // Get the real ID of the PDU and update all parts which were
-            // saved with the dummy ID.
+            // saved with the placeholder ID.
             msgId = ContentUris.parseId(res);
         }
 
         values = new ContentValues(1);
         values.put(Part.MSG_ID, msgId);
         SqliteWrapper.update(mContext, mContentResolver,
-                Uri.parse("content://mms/" + dummyId + "/part"),
+                Uri.parse("content://mms/" + placeholderId + "/part"),
                 values, null, null);
         // We should return the longest URI of the persisted PDU, for
         // example, if input URI is "content://mms/inbox" and the _ID of