Update language to comply with Android’s inclusive language guidance

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

Bug: 161896447
Change-Id: I56dd8778516103367dc17ae55bdff4457185de46

samples/MultiClientInputMethod/src/com/example/android/multiclientinputmethod/ClientCallbackImpl.java

@@ -164,10 +164,10 @@ final class ClientCallbackImpl implements MultiClientInputMethodServiceDelegate.
             mDelegate.setActive(mClientId, true /* active */);
         }
         if (inputConnection == null || editorInfo == null) {
-            // Dummy InputConnection case.
+            // Placeholder InputConnection case.
             if (window.getClientId() == mClientId) {
                 // Special hack for temporary focus changes (e.g. notification shade).
-                // If we have already established a connection to this client, and if a dummy
+                // If we have already established a connection to this client, and if a placeholder
                 // InputConnection is notified, just ignore this event.
             } else {
                 window.onDummyStartInput(mClientId, targetWindowHandle);