Scaffolding for custom RNDT shell binary (#52357)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/52357

Changelog: [Internal]

Adds a hyper-minimal build script using `electron/packager` that produces custom binaries for the experimental React Native DevTools standalone shell. The main user-facing benefit of this is replacing the Electron name and icon with our own branding.

NOTE: `electron/packager` is designed to include the application code in the resulting binary. This is arguably overkill for us - the current launch model of `electron src/electron/index.js` is actually wholly sufficient for what we need - but I decided to go with the grain of the available tooling for simplicity.

Icon design courtesy of huntie. 🙏

Reviewed By: huntie

Differential Revision: D77591742

fbshipit-source-id: a968465df4f54fba54c874b6300788e151600ed7