Empty init functions generated for side-effect-free ESM modules

Nobody has claimed this yet.

ESBuild seems to generate empty "module init" functions even for side-effect free ESM modules.

Given a module `src/utils/is-equal.mts`:

```ts
export function isEqual(a, b) {
// ...
}
```

What ends up in the generated bundle is (in the root scope):

```js
// src/utils/is-equal.mts
function isEqual(a, b) {
// ...
}
var init_is_equal = __esm({
"src/utils/is-equal.mts"() {
"use strict";
}
});
```

And then `init_is_equal` is called everywhere that `isEqual` is imported. What is causing this? I would not expect `init_is_equal` to be present. It does this for some modules but not others.

Config
- esbuild@0.21.3
- `platform: 'node', format: 'esm', target: 'node20'`
- Entire application is ESM and side-effect free (`"sideEffects: false"` in `package.json`) but some dependencies are CJS

Start by reproducing the behavior with the side-effect-free module in src/utils/is-equal.mts and the stated platform, format, and target settings. Inspect the generated bundle around init_is_equal and compare modules that do and do not receive an init function. Done means identifying the cause and establishing the expected generated output.

Written by the indexing model from the issue text.