update rollup from 2.35.1 (2020-12-14) to at least 3.16.0 (2023-02-17), or ideally latest (4.6.1, 2023-11-30)

Splitting this off as a new issue so it can be tracked more easily. See the original issue for more context:

> `output.sourcemapIgnoreList` was added to `rollup` in `3.16.0` (`2023-02-17`):
>
> - https://github.com/rollup/rollup/blob/master/CHANGELOG.md#3160
> - > Support `output.sourcemapIgnoreList` option to mark file sources as ignored in the `x_google_ignoreList` attribute of the resulting sourcemap (rollup/rollup#4848)
>
> `microbundle` is using a super outdated version of `rollup` (`2.35.1`) from `2020-12-14`:
>
> - https://github.com/developit/microbundle/blob/c76c41f8317611f7592d8e44c569e8083076f25f/package.json#L102
>
> So before we can implement this change, we'll need to upgrade to a modern version of `rollup`.
>
> _Originally posted by @0xdevalias in https://github.com/developit/microbundle/issues/1066#issuecomment-1837821773_

`microbundle` is currently using `rollup` `2.35.1` (`2020-12-14`):

- https://github.com/rollup/rollup/blob/master/CHANGELOG.md#2351

`output.sourcemapIgnoreList` (required to implement #1066) support was added in `3.16.0` (`2023-02-17`):

- https://github.com/rollup/rollup/blob/master/CHANGELOG.md#3160

Latest version (at time of writing) is `4.6.1` (`2023-11-30`):

- https://github.com/rollup/rollup/blob/master/CHANGELOG.md#461

Start with the Rollup dependency in package.json at the referenced line, then review the Rollup changelogs for changes between 2.35.1 and the target version. Update Rollup to at least 3.16.0, ideally 4.6.1, while checking that microbundle still builds and that the upgrade enables the output.sourcemapIgnoreList work required by #1066.

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