aapt: Use a std::map instead of a SortedVector

Android's SortedVectorImpl uses arrays that it must
insert into the middle of.  Each insertion is O(N) time
because it must move on average half the elements of
the array to make room for the new element.  That is,
O(N^2) time to build this sorted vector.

std::map on the other hand normally uses red/black
trees and has a cost of NlogN to add N elements to it.

Change-Id: I5da0363ba806ab615b2aad0fb2a43ef9a9bec327