Optimize lookup of quickening data.

Use the debug_info_off_ of CodeItem to store the quickening
offset in the vdex.

Impact:
- Code size almost unchanged (1 word saved per dex file in a vdex)
- GetQuickenedInfoOf doesn't show up in simpleperf during app startup

Test: test.py, run-libcore-tests, run-jdwp-tests
Test: 628-vdex
Change-Id: I15c3151feb58980a4c4d7469ca02728e94d36c07