WIP: feature: use WorkerLimit to parallelize one-shot mode

This PR extracts the parallel part of --make into GHC.Driver.WorkerLimit, then makes one-shot compilation in GHC.Driver.Pipeline use it.

Notably, cabal uses one-shot compilation for foreign sources, so in conjunction with an MR to cabal (https://github.com/haskell/cabal/pull/9872), this makes building foreign sources "just as parallel" as building Haskell sources, with the exception that they are compiled in a separate pass after Haskell sources due to --make not handling them natively.

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