[res] Make type iteration more efficient in aapt2

The iterator type that is only used in aapt2 currently
used to perform a binary search for every dereferencing call of
a sparse type table, while it knows for sure the position of the
next element in constant time.

+ Add a test for a sparse type iteration

Test: atest libandroidfw_tests
Flag: EXEMPT bugfix / refactor
Change-Id: I70f74b1a1cfb4deffd1592a87c31501388eaf46c