[llvm] [Lit][NFC] Refactor shell environment functionality and in-process builtins from TestRunner.py into new modules (Reopened) (PR #177358)

[Orlando Cazalet-Hyams via llvm-commits]

OCHyams wrote:

Reverted due to tripping the bots: https://github.com/llvm/llvm-project/pull/193740

https://github.com/llvm/llvm-project/pull/177358