feat: create exit handler class

[lukekarrys]

This PR refactors exit-handler.js to be a class so that it can more easily track its internal state. It uses this state to now fully distinguish between 3 states: npm never being set, npm not loaded, and exit handler never called. There are some new error messages shown via console.error if we know we are in an unexpected state.

This also continues the refactoring started in #7415 to separate concerns between npm and CLI. Identifying the error message and logging it have been move to npm but catching that error and setting the process.exitCode are still handled in exit-handler.js and cli/entry.js.

It also moves command.cmdExec to npm since it never called from within any command instance. This lets npm only ever call command.exec or command.workspaceExec now.

[wraithgar]

this newline is present in most other situations where the complete log message is displayed.

[wraithgar]

Testing locally this newline is now gone altogether in those other situations. Consistency is the thing here so we're good.

[lukekarrys]

Yes, glad you noticed. I couldn't find the true historical reason for this, but in refactoring I'm not confident we always display at least something to the user in all cases (even weird ones like npm is never set and then we error). But since this is truly just a display oriented newline, I wanted to remove it.