GHC should support printing -O* as list of optimization flags with same semantics

Related: #20500 (closed)

This issue is a feature request to make GHC support printing a list of optimization flags that will compose back into the same optimization pipeline as -O/-O2. This feature would be useful for debugging optimization bugs, since one can shrink the flag list to a minimal on the bug repro and can more easily spot the crime scene by inspecting the IR dumps.

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