add webdirt drum samples to prebake for general availability

[larkob]

This loads all default webdirt samples via prebake, so you can play a few drum samples with out as well as webdirt. This is mostly to make Strudel more beginner-friendly, but also so you can easily apply webaudio methods like velocity that webdirt doesn't support yet.

[larkob]

I'm using the experimental fetch feature (supported in node 16 LTS and 18), so there's no need to keep track of changes to the EmuSP12.json file that's coming from the webdirt repo. However, this will break possible compatibility with earlier versions of node.