Added index type of dex byte instructions.

Rationale:
The information was already in the instruction_list but not
exposed as enum through a getter. This CL adds that ability.
This information is needed by the upcoming Art-based dexdump.

NOTE:
Added "Index" to the enum constants naming convention.

NOTE:
Fixed few incorrect quickened entries in instruction_list.

Bug: 17442393

Change-Id: Ica18ae43135f78f29e9832f5a101d497e54724cf