SparseDoubleArray

Introduces a SparseDoubleArray class.
It is based on a SparseLongArray, storing the double values
in the bits of the long in the SparseLongArray.

This is a hidden class.
Not all long-term desired features of SparseDoubleArray
have necessarily been implemented here; only the ones needed
right now have been written.

Bug: 182845832
Test: atest BatteryStatsTests
Test: atest FrameworksCoreTests:android.util.SparseDoubleArrayTest
Change-Id: Id68b22328f2660839e2005990766d99140b00c16