`performance.now()` time doesn't incement on locally running workerd instances

As a library author, I would like to know that the assumptions I'm making about which operations are fast and which are slow apply to workerd. However, the security mitigatons documented in [Performance and timers](https://developers.cloudflare.com/workers/runtime-apis/performance/#performancenow) apply to locally running workerd instances as well, preventing any insight into workerd's performance characteristics.

Hopefully, the normal behavior of the `performance` global can be restored with either a command-line flag or as a field in the capnp configuration.

- The idea was floated in https://github.com/cloudflare/workerd/issues/390#issuecomment-1645567766 by @jasnell. I'm hoping this issue can be used to formally track its progress.