Add alloctop command-line tool

Add a command-line helper tool to parse /proc/allocinfo.

Bug: 384777823
Test: adb shell ls /system/bin/alloctop
Change-Id: I7a278cb74c62dad5d5b48bd5d1a095f2d80fd912
Signed-off-by: Alessio Balsini <balsini@google.com>