Reduce memory usage.

1. Make sure strings are interned so that memory isn't wasted on duplicate
   strings.
2. Most of the memory used by the TARE system was made up of the
   Transaction objects. The Transaction history is only kept for
   debugging purposes, so it can be reduced without affecting the
   policy. Reduce the number of transactions kept in memory by 92% for
   user builds to reduce the memory used by the TARE system by 90-92%.

Bug: 288479057
Test: atest frameworks/base/services/tests/mockingservicestests/src/com/android/server/tare
Test: atest frameworks/base/services/tests/servicestests/src/com/android/server/tare
Change-Id: Ic12a54a3d12be60a7fe20bb62931e8f2e62f1475