This work prepares for `turbopack build` by extracting code common between dev and build, such as asset context.

This also makes the cli accept a variadic list of entries rather than an unnamed directory parameter. The project directory is now available under `--dir` or `-d`.

Test Plan: `cargo run -p turbopack-cli dev` with a `src/index.js` present and `cargo run -p turbopack-cli dev src/entry.js` with `src/entry.js` present.

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…e-cli

…dularize-cli

…mith/modularize-cli

…e-cli

…dularize-cli

…mith/modularize-cli

…e-cli

…dularize-cli

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