Use @EnforcePermission for IIMM#addVirtualStylusIdForTestSession()

This CL manually migrates

  IInputMethodManager#addVirtualStylusIdForTestSession(),

which was added recently [1], from manual permission check with

  Context#enforceCallingPermission(INJECT_EVENTS)

to code-generation check with

  @EnforcePermission("INJECT_EVENTS").

There should be no observable semantic behavior change in this CL.

 [1]: I7399c0a56c04f024d65c16d459818cc2c5cdbc7f
      d96ef57bc4

Bug: 34886274
Bug: 210039666
Bug: 232058525
Bug: 237316307
Test: atest CtsInputMethodTestCases:InputMethodManagerTest#testShowInputMethodPickerFromSystemProtection
Change-Id: Ida227d417496dd91c071c38ca0be003529764de4

core/java/com/android/internal/view/IInputMethodManager.aidl

@@ -123,6 +123,7 @@ interface IInputMethodManager {
     boolean isStylusHandwritingAvailableAsUser(int userId);
 
     /** add virtual stylus id for test Stylus handwriting session **/
+    @EnforcePermission("INJECT_EVENTS")
     @JavaPassthrough(annotation="@android.annotation.RequiresPermission(value = "
             + "android.Manifest.permission.INJECT_EVENTS)")
     void addVirtualStylusIdForTestSession(in IInputMethodClient client);

services/core/java/com/android/server/inputmethod/InputMethodManagerService.java

@@ -4465,12 +4465,9 @@ public final class InputMethodManagerService extends IInputMethodManager.Stub
      * a stylus deviceId is not already registered on device.
      */
     @BinderThread
-    @RequiresPermission(Manifest.permission.INJECT_EVENTS)
+    @EnforcePermission(Manifest.permission.INJECT_EVENTS)
     @Override
     public void addVirtualStylusIdForTestSession(IInputMethodClient client) {
-        mContext.enforceCallingPermission(
-                Manifest.permission.INJECT_EVENTS,
-                "Using addVirtualStylusIdForTestSession() requires INJECT_EVENTS.");
         int uid = Binder.getCallingUid();
         synchronized (ImfLock.class) {
             if (!canInteractWithImeLocked(uid, client, "addVirtualStylusIdForTestSession")) {