Add script to dump llvm/eggccir for benchmarks

[rtjoa]

See the output here: https://github.com/egraphs-good/eggcc/tree/script-output/benchmarks/for_debugging/passing

To regenerate, go to benchmarks/for_debugging then:

#             input file                         output dir
./dump_one.sh ../passing/bril/core/bitshift.bril passing/bril/core
# all benchmarks:
./dump_all.sh