Introduce InputMethodSubtypeArray for memory efficient IPCs

This CL introduces InputMethodSubtypeArray which compresses
multiple instances of InputMethodSubtype to reduce the risk
of TransactionTooLargeException during IPCs.

There are some IMEs which rapidly adding new subtypes into
their supported language list. One problem here is that each
instance of InputMethodInfo internally owns the list of
supported subtypes. Basically it requires additional
200 ~ 300 bytes for each subtype when InputMethodInfo is
transffered via IPCs. We should keep the size less than
100 KB in typical scenario.

With this CL, the list of InputMethodSubtype is marshalled
with GZIP compression. Approximately one InputMethodInfo is
marshalled within 10 KB even when it has 100 subtypes.

No negative performance impact is observed so far. The cost of
decompression seems to be compensated by another optimization
in this CL. Actually marshalling cost is reduced with this CL
by caching the compressed data on demand.

BUG: 12954290
Change-Id: Ibb2940fcc02f3b3b51ba6bbe127d646fd7de7c45