Move opcode names into OpcodeInfo.

This also allowed me to remove the Instruction argument from the
CodeReader visitor methods. Per previous discussion, this also gets
rid of the redundant argument output in FindUsages. I can clean up
CodeReader some more in a follow-up.

Change-Id: I7a65e8d74498e201fd169cddde0d1f19d6f33f81
8 files changed