[IMP] bundling: Improve owl bundling process and output (#751)

The bundle pipeline can use a bit of a improvement:

Most of the process is moved from npm scripts to rollup.
Add package keys to smooth out the use of bundlers of the end users.
(Rollup by example check amongst others the main, module and browser key
to import the right version of a lib when needed).
Refactor rollup logic to make it more modular.
Add bundled module formats.
Add comments to tsconfig to see more clearly what's possible.
Add reference tag to help @types discovery in test files.

Co-authored-by: Simon Genin (ges) <ges@odoo.com>

rollup.config.js

@@ -1,14 +1,69 @@
-import { version } from "./package.json";
+import pkg from "./package.json";
 import git from "git-rev-sync";
+import typescript from 'rollup-plugin-typescript2';
+import { terser } from "rollup-plugin-terser";
 
-// rollup.config.js
-export default {
-  input: "dist/owl/index.js",
-  output: {
-    file: "dist/owl.js",
-    format: "iife",
-    name: "owl",
-    extend: true,
-    outro: `exports.__info__.version = '${version}';\nexports.__info__.date = '${new Date().toISOString()}';\nexports.__info__.hash = '${git.short()}';\nexports.__info__.url = 'https://github.com/odoo/owl';`
+const name = "owl"
+const extend = true
+
+/**
+ * Meta data to be added on the __info__ object. 
+ * Used to let external tools know the current owl version.
+ */
+const outro =  `
+__info__.version = '${pkg.version}';
+__info__.date = '${new Date().toISOString()}';
+__info__.hash = '${git.short()}';
+__info__.url = 'https://github.com/odoo/owl';
+`
+
+/**
+ * Generate from a string depicting a path a new path for the minified version.
+ * @param {string} pkgFileName file name 
+ */
+function generateMinifiedNameFromPkgName(pkgFileName) {
+  const parts = pkgFileName.split('.')
+  parts.splice(parts.length - 1, 0, "min");
+  return parts.join('.');
+}
+
+/**
+ * Get the rollup config based on the arguments
+ * @param {string} format format of the bundle
+ * @param {string} generatedFileName generated file name
+ * @param {boolean} minified should it be minified
+ */
+function getConfigForFormat(format, generatedFileName, minified = false) {
+  return {
+    file: minified ? generateMinifiedNameFromPkgName(generatedFileName) : generatedFileName,
+    format: format,
+    name: name,
+    extend: extend,
+    outro: outro,
+    plugins: minified ? [terser()] : []
   }
+}
+
+export default {
+  input: "src/index.ts",
+  output: [
+
+    /**
+     * Read about module formats:
+     *  https://auth0.com/blog/javascript-module-systems-showdown/
+     *  https://medium.com/@kelin2025/so-you-wanna-use-es6-modules-714f48b3a953
+     */
+
+    getConfigForFormat('esm', pkg.module),
+    getConfigForFormat('esm', pkg.module, true),
+    getConfigForFormat('cjs', pkg.main),
+    getConfigForFormat('cjs', pkg.main, true),
+    getConfigForFormat('iife', pkg.browser),
+    getConfigForFormat('iife', pkg.browser, true),
+  ],
+  plugins: [
+    typescript({
+      useTsconfigDeclarationDir: true
+    }),
+  ]
 };