Use quicksort to sort the string pool.

The current implementation of Vector::sort uses insertion sort
on the assumption that the data is mostly sorted.  It isn't.

This change brings the total time spent sorting packages by config
down to 500ms from about 93 seconds.

Bug: 6186278
Change-Id: Iec8da11e09297acd6c73733d063b0fa9dacf69f7