{in: '',out: ''} entrypoints should support entryNames

When using the `{in: '', out: ''}` entrypoint format, would it be possible to add the ability to also set a `name` option that would mirror the behaviour of [`entryNames`](https://esbuild.github.io/api/#entry-names)?

Start by reading the esbuild API documentation for entryNames and the `{in: '', out: ''}` entrypoint format. Trace how this entrypoint form is handled in the Go implementation and identify the relevant existing tests. Done means the format accepts a name option and applies entryNames-equivalent behavior without changing existing input/output handling.

Written by the indexing model from the issue text.