This change refactors the 'split blocks' transformation so that an
instruction is identified via a base, opcode, and number of those
opcodes to be skipped when searching from the base, as opposed to the
previous design which used a base and offset.
This transformation can introduce an instruction that uses
OpCopyObject to make a copy of some other result id. This change
introduces the transformation, but does not yet introduce a fuzzer
pass to actually apply it.
With this pass, the fuzzer can split blocks in the input module. This
is mainly useful in order to give other (future) transformations more
opportunities to apply.
