[pm] revert changes to mAppIds

SparseArray has O(nlog(n)) look up time because it relies on binary
search. Reverting back to using an index-based ArrayList for non-system
apps because n might be big.

BUG: 223215503
Test: atest com.android.server.pm.PackageManagerSettingsTests
Change-Id: I5ac1521bb32ef7930460a14fec783e32ddfe663c