Is it possible to customize the [dir] in entryNames?

First thank you so much for esbuild. It is an absolute joy to work with!

### Issue

I'm running into an issue where I need to bundle some files from a directory in `node_modules`.

```js
await build({
entryPoints: [
'./src/**/*.page.js',
'./node_modules/some-module/files/**/*.page.js'
],
bundle: true,
entryNames: '[dir]/[name]',
outbase: "./",
outdir: './dist',
platform: 'node',
format: 'esm',
});
```

This code works, but the output in `./dist` ends up containing a folder called `node_modules/`, which causes node to think that files under that path are actual node modules. Since that output directory doesn't contain a package.json, node thinks it's a CommonJS module and gets confused to why there's an ESM file in there.

### Minimal reproduction

https://github.com/ryanto/esbuild-entrynames-dir

### Temp fix I'm using

As a temporary fix, I have dropped `[dir]` from `entryNames` so that no folder named `node_modules` will end up in `./dist`. I am using `entryNames: [name]-[hash]`, but I am worried I am going to get a collision due to the large number of files I'm building with similar names. I would love to add [dir] back because it makes debugging and viewing build output easier for me.

It would be great if I could customize the name of the output file to ensure that there's no `node_modules` name in it's path. I think this might be possibility related to the `onEmit` plugin API mentioned in https://github.com/evanw/esbuild/issues/553

Again thank you so much for esbuild!

Start with the linked minimal reproduction and the entryNames/outbase options shown in the issue. Trace how [dir] produces the node_modules directory and determine what customization is needed; done means output paths can avoid node_modules while retaining useful directory structure without collisions.

Written by the indexing model from the issue text.