[NFC][llvm-exegesis] Refactor ResolvedSchedClass & friends
Summary:
`ResolvedSchedClass` will need to be used outside of `Analysis`
(before `InstructionBenchmarkClustering` even), therefore promote
it into a non-private top-level class, and while there also
move all of the functions that are only called by `ResolvedSchedClass`
into that same new file.
Reviewers: courbet, gchatelet
Reviewed By: courbet
Subscribers: mgorny, tschuett, mgrang, jdoerfert, llvm-commits
Tags: #llvm
Differential Revision: https://reviews.llvm.org/D59993
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@357259
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