Overriding outbase

Hi there!

Given the following:

```js
await esbuild.build({
outbase: "app/javascript"
})
```

```js
// app/javascript/index.js
import ""
```

Produces the following:

```
_.._/_.._/node_modules/pkg
```

What I would like it to produce:

```
node_modules/pkg
```

Is there a way to use an `onResolve` plugin to either mimic an "outbase" and ignore it for "node_module" imports, or is there a way to override "outbase" for specific imports?

The payload names no files or tests. Start by reproducing the esbuild.build configuration with outbase and the onResolve plugin, then trace resolver and output-path handling; done means the reported node_modules import is not prefixed by outbase, with coverage for this case.

Written by the indexing model from the issue text.