Import gson 2.9.1 am: e42ae74108

Original change: https://android-review.googlesource.com/c/platform/external/gson/+/2181028

Change-Id: I102a16c121001b22602d49542f961b46f3828648
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>