Add support for loading snapshots and update IGamesCallbacks and IGam…

[NepMods]

Games: Fix snapshot transaction codes so game data (cloud saves) works

Evidence

Transaction codes were extracted from the real Play Games SDK AAR
(com.google.android.gms:play-services-games) via the AIDL Stub onTransact
switch and the client callback implementations, and cross-checked against two SDK
revisions:

Callback / method	microG (before)	Real SDK
onSnapshotsLoaded(DataHolder)	— (missing)	12001
onResolveSnapshotHead(DataHolder, Contents)	12003	12004
commitSnapshotResult(DataHolder)	12004	12005
getSelectSnapshotIntent(...)	12000	12001
loadSnapshots(...)	12001	12002
commitSnapshot(...)	12006	12007
discardAndCloseSnapshot(Contents)	12018	12019
resolveSnapshotHead(...)	15000	15001

The callback mapping is confirmed by the client implementations, e.g.
zzbi.zzt(DataHolder) (12001) builds AnnotatedData<SnapshotMetadataBuffer>,
zzbv.zzs(DataHolder, Contents) (12004) handles snapshot open, and
zzag.zzp(DataHolder) (12005) builds a SnapshotMetadata commit result.

Changes

• play-services-games/.../IGamesCallbacks.aidl
  • Add onSnapshotsLoaded(in DataHolder data) = 12001.
  • Correct onResolveSnapshotHead → 12004 and commitSnapshotResult → 12005.
• play-services-games/.../IGamesService.aidl
  • Correct the snapshot service codes listed above.
• play-services-core/.../games/GamesService.kt
  • Implement loadSnapshots(): request the games_lite + Drive appfolder token,
    fetch snapshots via SnapshotsDataClient.loadSnapshotData(), build a
    DataHolder over the player/game/snapshot columns, and deliver it via
    onSnapshotsLoaded (failure returns a non-OK status holder).
  • Populate the snapshot metadata row in resolveSnapshotHead()'s DataHolder
    (id, unique name, title/description, timestamp, duration, progress, device,
    cover image) instead of returning only the player row.
  • discardAndCloseSnapshot() now closes the Contents file descriptor.