fix: allow string modes in createEditSession types

## Summary - Allow `ace.createEditSession` to accept string mode IDs in the generated public TypeScript declaration. - Add package type coverage for passing a string mode to `createEditSession`. Fixes #5946 ## Testing - `bash tool/test-npm-package.sh` - `npm run typecheck` - `node_modules/.bin/tsc --noImplicitAny --strict --noUnusedLocals --noImplicitReturns --noUnusedParameters --noImplicitThis ace.d.ts` - `npx eslint src/ace.js` - `npm run update-types` - `git diff --check` By submitting this pull request, I confirm that you can use, modify, copy, and redistribute this contribution, under the terms of your choice. [Open kitchen-sink @ f03a1a4cdd1d6350c2674b263bf78d4fa3dd2604](https://raw.githack.com/cyphercodes/ace/f03a1a4cdd1d6350c2674b263bf78d4fa3dd2604/kitchen-sink.html)