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
The previous details were showing their age, e.g. mentions about browsers
not supporting ES2015. The story with ES modules is more complex as it's also
about loaders but to keep the README simple, let's just make it more up to date
with typical usage.
Closes gh-5108
Use a dist README fixture kept in the jQuery repository instead of modifying
an existing one. This makes the jQuery repository the single source of truth
when it comes to jQuery releases and it makes it easier to make changes to
README without worrying how it will affect older jQuery lines.
The commit also ES6ifies build/release.js & build/release/dist.js
Closes gh-4614
