Could not resolve file without extension from node_modules when using ts and tsx loader for js files

I have a very specific problem regarding ts and tsx loader and imports from node_modules that do not have extension specified.
Steps or files to reproduce:

package.json:
```
{
"name": "esbuild-test",
"main": "app.js",
"scripts": {
"build": "node build.mjs"
},
"devDependencies": {
"esbuild": "^0.24.0"
},
"dependencies": {
"core-js": "^3.38.1",
"regenerator-runtime": "^0.14.1"
}
}
```

app.jsx:
```
import 'core-js/stable'
//import 'regenerator-runtime/runtime'

console.log('Hello world!');
```

build.mjs:
```
import esbuild from 'esbuild'

await esbuild.build({
entryPoints: ['app.jsx'],
outfile: 'output.js',
bundle: true,
loader: {
'.jsx': 'tsx',
'.js': 'ts',
},
})
```

When I run `node build.mjs` I get this error: `Could not resolve "core-js/stable"`.
Seems like a problem with resolving file `index.js` in `core-js/stable` folder. If I specify this file directly it works, but then it fails to resolve other imports form this file.

Likewise, if I import a file from `node_modules` without extension - in my case it was `import 'regenerator-runtime/runtime'` - the build fails with `Could not resolve "regenerator-runtime/runtime"` but if I provide full file name with extension `import 'regenerator-runtime/runtime.js'`, it works.

By gradual elimination and trial-error method I discovered, that it may have something to do with `tsx` and `ts` loader. If I comment out either `'.jsx': 'tsx'` or `'.js': 'ts'` line from build.mjs the resolution and build works.
However, I need tsx transformation, because of experimental decorators that we are using through all of our project.

This also happes when I import some library which has a file without extension in its `"main"` field in `package.json`
(eg. `"main": "es/index"`)

Interestingly, this setup was working in esbuild 0.19.* and stopped working in 0.20 (tested also all newer versions but without success). So I assume it may have something to do with 'Reorder implicit file extensions within node_modules' [change in 0.20.0](https://github.com/evanw/esbuild/blob/main/CHANGELOG.md#0200)

I also tested multiple node versions 19, 20, 21, 22 all with the same results.

Please, can you confirm if this is a bug or just some incorrect setting, in which case please point me to the right direction.

Start by running the provided node build.mjs reproduction with esbuild 0.20+ and compare it with 0.19.*. Inspect the resolver behavior around extensionless imports in node_modules and the 0.20.0 changelog entry “Reorder implicit file extensions within node_modules.” Done means both ts and tsx loaders resolve the shown core-js and regenerator-runtime imports without requiring explicit extensions.

Written by the indexing model from the issue text.