benchmark: rewrite detect-esm-syntax benchmark

Syntax detection has been unflagged so it's no longer meaningful
to toggle the detection based on CLI flags. It was also previously
benchmarking cached module imports which isn't very meaningful
for subsequent loads. This patch updates the benchmark to toggle
the detection based on the presence of type field in the package.json,
and generates fixtures to benchmark fresh module loads.

benchmark/esm/detect-esm-syntax.js

@@ -4,34 +4,33 @@
 // We use the TypeScript fixture because it's a very large CommonJS file with no ESM syntax: the worst case.
 const common = require('../common.js');
 const tmpdir = require('../../test/common/tmpdir.js');
-const fixtures = require('../../test/common/fixtures.js');
-const scriptPath = fixtures.path('snapshot', 'typescript.js');
 const fs = require('node:fs');
 
 const bench = common.createBenchmark(main, {
-  type: ['with-module-syntax-detection', 'without-module-syntax-detection'],
+  type: ['with-package-json', 'without-package-json'],
   n: [1e4],
-}, {
-  flags: ['--experimental-detect-module'],
 });
 
-const benchmarkDirectory = tmpdir.fileURL('benchmark-detect-esm-syntax');
-const ambiguousURL = new URL('./typescript.js', benchmarkDirectory);
-const explicitURL = new URL('./typescript.cjs', benchmarkDirectory);
-
 async function main({ n, type }) {
   tmpdir.refresh();
+  fs.mkdirSync(tmpdir.resolve('bench'));
 
-  fs.mkdirSync(benchmarkDirectory, { recursive: true });
-  fs.cpSync(scriptPath, ambiguousURL);
-  fs.cpSync(scriptPath, explicitURL);
-
-  bench.start();
-
+  let loader = '';
+  const modules = [];
   for (let i = 0; i < n; i++) {
-    const url = type === 'with-module-syntax-detection' ? ambiguousURL : explicitURL;
-    await import(url);
+    const url = tmpdir.fileURL('bench', `mod${i}.js`);
+    fs.writeFileSync(url, `const foo${i} = ${i};\nexport { foo${i} };\n`);
+    loader += `import { foo${i} } from './mod${i}.js';\n`
+    modules.push(url);
   }
+  const loaderURL = tmpdir.fileURL('bench', 'load.js');
+  fs.writeFileSync(loaderURL, loader);
 
+  if (type === 'with-package-json') {
+    fs.writeFileSync(tmpdir.resolve('bench', 'package.json'), '{ "type": "module" }');
+  }
+
+  bench.start();
+  await import(loaderURL);
   bench.end(n);
 }