Support building for externally shared js builtins

Initial support for loading unbundled module in `AddExternalizedBuiltin`.

- Reduces downstream distribution package size (by not shipping wasm twice
  and not base64-encoding it)
- Provides a cleaner stacktrace
- Easier to patch

To enable this, pass `EXTERNAL_PATH=/global/node_modules/cjs-module-lexer`
to `build.js`.
You shall also pass this path to `--shared-builtin-cjs_module_lexer/dist/lexer-path`
in Node.js's `configure.py`, with the extra `/dist` part in the path.

Signed-off-by: Zephyr Lykos <git@mochaa.ws>

build.js

@@ -1,25 +1,72 @@
 const fs = require('fs');
-const terser = require('terser');
+const { buildSync } = require('esbuild');
 
-const MINIFY = true;
+const { EXTERNAL_PATH } = process.env;
+const MINIFY = !EXTERNAL_PATH;
 
 try { fs.mkdirSync('./dist'); }
 catch (e) {}
 
 const wasmBuffer = fs.readFileSync('./lib/lexer.wasm');
-const jsSource = fs.readFileSync('./src/lexer.js').toString();
 const pjson = JSON.parse(fs.readFileSync('./package.json').toString());
 
-const jsSourceProcessed = jsSource.replace('WASM_BINARY', wasmBuffer.toString('base64'));
+buildSync({
+  entryPoints: ['./src/lexer.js'],
+  outfile: './dist/lexer.mjs',
+  bundle: true,
+  minify: MINIFY,
+  platform: 'node',
+  format: 'esm',
+  banner: {
+    js: `/* cjs-module-lexer ${pjson.version} */`
+  },
+  define: EXTERNAL_PATH ? {
+    WASM_BINARY: 'undefined',
+    EXTERNAL_PATH: `'${EXTERNAL_PATH}'`,
+  } : {
+    WASM_BINARY: `'${wasmBuffer.toString('base64')}'`,
+    EXTERNAL_PATH: 'undefined'
+  }
+})
 
-const minified = MINIFY && terser.minify(jsSourceProcessed, {
-  module: true,
-  output: {
-    preamble: `/* cjs-module-lexer ${pjson.version} */`
+if (EXTERNAL_PATH) {
+  buildSync({
+    stdin: {
+      contents: `'use strict';
+let lazy;
+async function init () {
+  if (!lazy) {
+    lazy = await import(require('node:url').pathToFileURL(require('node:module').createRequire('${EXTERNAL_PATH}/dist/lexer.js').resolve('./lexer.mjs')));
   }
-});
+  module.exports = lazy;
+  return lazy.init();
+}
+
+function parse (source, name = '@') {
+  if (!lazy)
+    throw new Error('Not initialized');
+
+  return lazy.parse(source, name);
+}
 
-if (minified.error)
-  throw minified.error;
+module.exports = { init, parse };`,
+      loader: 'js',
+    },
+    outfile: './dist/lexer.js',
+    minify: MINIFY,
+    platform: 'node',
+    format: 'cjs',
+  });
+} else {
+  buildSync({
+    entryPoints: ['./dist/lexer.mjs'],
+    outfile: './dist/lexer.js',
+    minify: MINIFY,
+    platform: 'node',
+    format: 'cjs',
+    banner: {
+      js: `/* cjs-module-lexer ${pjson.version} */`
+    }
+  })
+}
 
-fs.writeFileSync('./dist/lexer.mjs', minified ? minified.code : jsSourceProcessed);