walkProgram
walkProgramWithCfg
Fix a mistake in our (internal) types: `walkProgramWithCfg` was missing that elements can be `CfgVisitFn`. Also refactor the types for `walkProgram`, importing the original `VisitFn` and `EnterExit` types from where they're defined.
src-js
moves the generated code into src-js to keep the same pattern as oxlint