Build: migrate most grunt tasks off of grunt

Build: migrate most grunt tasks off of grunt

Updated tasks include:

- lint
- npmcopy
- build, minify, and process for distribution.
- new custom build command using yargs
- compare size of minified/gzip built files
- pretest scripts, including qunit-fixture, babel transpilation, and npmcopy
- node smoke tests
- promises aplus tests
- new watch task using `rollup.watch` directly

Also:

- upgraded husky and added the new lint command
- updated lint config to use new "flat" config format. See https://eslint.org/docs/latest/use/configure/configuration-files-new
- Temporarily disabled one lint rule until flat config is supported by eslint-plugin-import. See https://github.com/import-js/eslint-plugin-import/issues/2556
- committed package-lock.json
- updated all test scripts to use the new build
- added an express test server that uses middleware-mockserver (this can be used to run tests without karma)
- build-all-variants is now build:all

Close gh-5318