Build: Add `exports` to package.json, export slim & esm builds

Build: Add `exports` to package.json, export slim & esm builds

Summary of the changes:
* define the `exports` field in `package.json`; `jQuery` & `$` are also
  exported as named exports in ESM builds now
* declare `"type": "module"` globally except for the `build` folder
* add the `--esm` option to `grunt custom`, generating jQuery as an ECMAScript
  module into the `dist-module` folder
* expand `node_smoke_tests` to test the slim & ESM builds and their various
  combinations; also, test both jQuery loaded via a path to the file as well
  as from module specifiers that should be parsed via the `exports` feature
* add details about ESM usage to the release package README
* run `compare_size` on all built minified files; don't run it anymore on
  unminified files where they don't provide lots of value
* remove the remove_map_comment task; SWC doesn't insert the
`//# sourceMappingURL=` pragma by default so there's nothing to strip

Fixes gh-4592
Closes gh-5255