[llvm] [Passes] Manage extra passes using inner pass managers (NFC). (PR #119348)

[Arthur Eubanks via llvm-commits]

aeubanks wrote:

we need to figure out a way to represent these pass managers with the textual pipeline representation. it'll probably require something like https://github.com/llvm/llvm-project/blob/a8456c9a2fb36f7c3a69eaa296c3f5d23ec52fe5/llvm/lib/Passes/PassBuilder.cpp#L1530

https://github.com/llvm/llvm-project/pull/119348