require.main + multiple entrypoints

I believe this is a tsup issue, not an esbuild one, since CJS code splitting is a checked in esbuild plugin and uses sucrase.

The issue is that with multiple entry points, the generated `__require` helpers get put into their own chunk which breaks the `require.main === module` check.


Start by reproducing a tsup build with multiple entry points and CJS code splitting, then inspect the generated chunks and the placement of the __require helpers. Done means the generated output preserves the require.main === module check instead of moving the helpers into a separate chunk.

Written by the indexing model from the issue text.