Add fast string sharpening

String sharpening changes const strings to PC relative loads instead
of always going through the dex cache. This saves code size and
probably improves performance slightly.

Before: 49602992 system@framework@boot.oat
After: 49385904 system@framework@boot.oat

Pre-cursor to removing dex_cache_strings_ field from ArtMethod.

Bug: 17643507

Change-Id: I1787f48774631eee0accafeea257aa8d0e91e8d6
8 files changed