Track ImeTrackerService active capacity

This adds a maximum capacity for the number of simultaneously active
requests in ImeTrackerService. When this capacity is reached, updates
for currently active requests are allowed, however no new entries can be
created to start new active requests, until the capacity clears. This
will protect against too many repeated requests in a short time frame.

This also increases the maximum capacity for completed entries, such
that we can track a slightly longer history. This also helps in
verifying against updates on already completed tokens.

Flag: EXEMPT bugfix
Test: atest ImeTrackerServiceTest#testCannotCreateWhenActiveFull
Bug: 342111149
Change-Id: I83d1f7af540d61cc73410b667d6f97733a16f5c8