Chore: refactor config hash caching in CLIEngine (#9260)
Chore: refactor config hash caching in CLIEngine (#9260)

Previously, CLIEngine would store the last config object when executing on multiple files, as a performance optimization to avoid rehashing configs if the same config was used for multiple files.

This can be better implemented by using a WeakMap to map config objects to hash results.
scriptdaemon/eslint,brgibson/eslint,Trott/eslint,DavidAnson/eslint,BenoitZugmeyer/eslint,whitneyit/eslint,Moeriki/eslint,scriptdaemon/eslint,Aladdin-ADD/eslint,pvamshi/eslint,onurtemizkan/eslint,platinumazure/eslint,Trott/eslint,ABaldwinHunter/eslint,ABaldwinHunter/eslint,mzgol/eslint,onurtemizkan/eslint,Aladdin-ADD/eslint,kentcdodds/eslint,BenoitZugmeyer/eslint,ljharb/eslint,platinumazure/eslint,mzgol/eslint,kentcdodds/eslint,DavidAnson/eslint,eslint/eslint,pvamshi/eslint,eslint/eslint,whitneyit/eslint,brgibson/eslint,Moeriki/eslint,ljharb/eslint