[Feature]: Zero-Configuration Rslib

[colinaaa]

What problem does this feature solve?

Tools like pkgroll and microbundle offer zero-configuration support. It would be great if Rslib also supports using with zero-configuration.

What does the proposed API look like?

Rslib can be run without rslib.config.ts. Most of the configuration can be read from package.json.

• Read entry from main, module, umd and exports
• Read externals from dependencies, devDependencies and peerDependencies
• Read alias from package.json#imports

Or, maybe create a new tool Rspkg that uses Rslib with zero-configuration.

[fi3ework]

Yeah! Using package.json as the single source of truth is in plan. Rslib also should check the correctness with it when providing a rslib.config file. We may support autoExternal at first (tracked in https://github.com/web-infra-dev/rslib/issues/46).