[feature request] [`@rollup/plugin-html`] Ability to use HTML as entry point

[vadimkantorov]

As discussed in:

• Allow HTML as entry points rollup#2873 (comment)

It’s useful to have HTML as entry point for discovering depending JS packages (similarly to https://github.com/modernweb-dev/web/tree/master/packages/rollup-plugin-html/src).

It would also be great to have a single-html-file output mode (with JS bundle fully inlined).