Replace HashMap with ArrayMap in AppsFilterImpl

This saves memory in the system_server.
Additionally, this CL replaces iterators with for loops using
valueAt() to save further memory.

Test: adb shell am dumpheap `adb shell pidof system_server`
Test: then use ahat to manually inspect: http://screen/3dVis7RNst2SJp8
Bug: 254230758
Change-Id: Iada8859e7c04f6dde2d7d1fbc0ab730d6e035770