Rewrite of CursorWindow internals.

The original CursorWindow implementation was created in Android 1.0
and has remained relatively unchanged since then.  Unfortunately that
design results in very poor performance on large windows, since
reading or writing each FieldSlot is O(row/100) to traverse through
a chain of RowSlotChunks.  It's also memory-inefficient due to how
it allocates RowSlotChunks in 404 byte chunks, even when there's only
a single row to store.

This change is a complete redesign of the CursorWindow internals to
use a "heap-and-stack" style approach, where a "heap" of strings
and blobs increment up from the bottom of the window while a "stack"
of FieldSlots increment down from the top of the window.

The included benchmarks show the following improvements, ensuring
no regressions for small windows, while offering very dramatic
improvements for larger windows:

                Big cores      Little cores
4x4 cursor      no regression  no regression
1024x4 cursor   2.2x faster    2.0x faster
16384x4 cursor  48.5x faster   24.4x faster

Detailed unit testing is also included to ensure that the rewrite
behaves correctly.

Bug: 169251528
Test: atest libandroidfw_tests
Test: atest CtsDatabaseTestCases
Test: atest FrameworksCoreTests:android.database
Test: ./frameworks/base/libs/hwui/tests/scripts/prep_generic.sh little && atest libandroidfw_benchmarks
Test: ./frameworks/base/libs/hwui/tests/scripts/prep_generic.sh little && atest CorePerfTests:android.database.CrossProcessCursorPerfTest
Change-Id: I90dff31fd550130dae917a33e0e1fa684e15c107