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

4 files changed, 56 insertions, 0 deletions

diff --git a/dist-module/.eslintrc.json b/dist-module/.eslintrc.json
new file mode 100644
index 000000000..33335abd8
--- /dev/null
+++ b/dist-module/.eslintrc.json
@@ -0,0 +1,45 @@
+{
+	"root": true,
+
+	"parserOptions": {
+		"ecmaVersion": 2015,
+		"sourceType": "module"
+	},
+
+	"globals": {
+		"define": false,
+		"Symbol": false
+	},
+
+	"overrides": [
+		{
+			"files": "jquery{,.slim}.module.min.js",
+
+			"parserOptions": {
+				"ecmaVersion": 2015,
+				"sourceType": "module"
+			}
+		},
+
+		{
+			"files": "jquery{,.slim}.module.js",
+			"extends": "../.eslintrc-browser.json",
+
+			"parserOptions": {
+				"ecmaVersion": 2015,
+				"sourceType": "module"
+			},
+
+			"rules": {
+
+				// That is okay for the built version
+				"no-multiple-empty-lines": "off",
+
+				// When custom compilation is used, the version string
+				// can get large. Accept that in the built version.
+				"max-len": "off",
+				"one-var": "off"
+			}
+		}
+	]
+}
diff --git a/dist-module/jquery.node-module-wrapper.js b/dist-module/jquery.node-module-wrapper.js
new file mode 100644
index 000000000..bda9eb3d7
--- /dev/null
+++ b/dist-module/jquery.node-module-wrapper.js
@@ -0,0 +1,4 @@
+import jQuery from "../dist/jquery.js";
+const $ = jQuery;
+export { jQuery, $ };
+export default jQuery;
diff --git a/dist-module/jquery.node-module-wrapper.slim.js b/dist-module/jquery.node-module-wrapper.slim.js
new file mode 100644
index 000000000..900f32fc2
--- /dev/null
+++ b/dist-module/jquery.node-module-wrapper.slim.js
@@ -0,0 +1,4 @@
+import jQuery from "../dist/jquery.slim.js";
+const $ = jQuery;
+export { jQuery, $ };
+export default jQuery;
diff --git a/dist-module/package.json b/dist-module/package.json
new file mode 100644
index 000000000..3dbc1ca59
--- /dev/null
+++ b/dist-module/package.json
@@ -0,0 +1,3 @@
+{
+  "type": "module"
+}