Use ArrayMap to cache active subscriptions

Because we use ArrayMap to deduplicate active subscriptions.
Caching also needs to use ArrayMap, otherwise it will cause
index inconsistency.

Bug: 295124402

Change-Id: I4fa0efd1d35855d0ea7723ad6134213ab384cd4d
Signed-off-by: DingFei Song <v-dingfeisong@xiaomi.corp-partner.google.com>