Match return types for addFirst and addLast with List am: 9b651e268b

Original change: https://android-review.googlesource.com/c/platform/external/javaparser/+/2887806

Change-Id: I850a98407e656b3722d83dfc489b65354c7fc6e9
Signed-off-by: Automerger Merge Worker <[email protected]>