Port pow and float_power method_tests entries to OpInfos

[mruberry]

Part of the more general tracking issue #54261.

cc @mruberry @VitalyFedyunin @walterddr

[imaginary-person]

Trying to add the OpInfo for pow via #50999.

[krshrimali]

Hi, I would like to pick this up (porting float_power method_tests entries to OpInfos). Hoping that it doesn't coincide with anyone's plan, and if it does - please let me know. Thanks!