Event log profiling events represent the cost centre stack as a list of cost centre ids. Some tooling (e.g. [hs-speedscope](https://github.com/mpickering/hs-speedscope)) even relies on this representation. It would be useful if we had some way of getting cost centre ids via `GHC.Stack.CCS` so we could link samples from the program to samples in the event log. I think this will require a CLC proposal, which I've created [here](https://github.com/haskell/core-libraries-committee/issues/235). Patch is !11798.