Switch to source-built GSON. am: 8277d985a5 am: 81b5465030 am: a874cbd8df am: 9fda783a14

Original change: https://android-review.googlesource.com/c/platform/external/mobly-bundled-snippets/+/2198804

Change-Id: Icb0c7c579292d2eb27312c3328ed0afe487e324a
Signed-off-by: Automerger Merge Worker <android-build-automerger-merge-worker@system.gserviceaccount.com>