Do not preallocate memory in default constructor of Sparse.*Array

By heapdump examination this saves not-an-insignificant amount of
memory and significant amount of allocations.
Similar change was also introduced for ArrayList & HashMap
implementation in JDK8.

More details in go/if-xr-android-util-collections-lazy-init.

Bug: 272467748
Test: Verified system server heapdump
Change-Id: I849dbaa46e79eae0b61b93a7ab1f5d5ef8bfbf7f