AAPT2: Reorder link steps

AAPT2's link steps were writing the res/* files before optimizations to the
resource table were performed (such as version collapsing). This was causing
unreferenced res/* files to remain in the archive, even though they're no
longer necessary.

Bug: 30705740
Change-Id: I50d7943ef7429b14e46587093855c15d54038299