Roll forward new copy insertion pass.

Original cl: cl/174423881, rollback cl: cl/174505237.

This roll forward includes the following changes from the original to address various issues uncovered with the rollback:

(1) A fix for a problem with fusion instruction serialization was broken out and submitted separately (cl/176035108).

(2) A dataflow analysis fix was broken out and submitted separately (cl/176035108)

(3) Adding RunBenchmarks to our unit test main was broken out. Fix for uncovered segv in while_test_cpu benchmark in pending cl/176068232.

(4) Moved a cpu-specific copy-insertion pass into it's own file, and added tests.

(5) Renamed gpu/copy_insertion.* to gpu/gpu_copy_insertion.* to match cpu side.

PiperOrigin-RevId: 176658339