Add layout scheme to dexlayout for dex file reordering.

Currently takes startup classes from profile and groups them together
with the lowest class indexes. Moves the ClassDef, ClassData, and
CodeItem sections.

Results gathered from 5 second systrace of app startup (no other input):
Maps
base.vdex - 24.70MB -> 19.35MB (30.50MB file size)
base.odex - 13.22MB -> 12.82MB (13.22MB file size)
Running time of dex2oat: 27.5s -> 37.1s

Photos
base.vdex - 12.98MB ->  9.77MB (15.10MB file size)
base.odex -  6.84MB ->  6.24MB ( 6.84MB file size)
Running time of dex2oat: 15.6s -> 19.9s

Plus
base.vdex - 14.09MB -> 13.29MB (16.72MB file size)
base.odex -  2.47MB ->  2.47MB ( 2.47MB file size)
Running time of dex2oat: 14.1s -> 18.5s

Performance and memory tracking bug: b/33017139

Test: mm test-art-host-gtest-dexlayout_test
Bug: 29921113
Change-Id: Ib500ed353d71a606e2db0dd80378750c5f7b8e33