Use SWC as transpiler

[sparr]

This is a repeat of #1177.

My use case for swc is that I need to transpile to older ES versions, which afaik is out of scope for Bun. I'm currently using a Bun build plugin to run tsc on the js build artifacts, but that's much slower than swc. I'm about to try getting it working with running swc in the same way, but having it integrated as a transpiler option would be much cleaner.

[RiskyMH]

Is there a reason you can't use swc directly? I feel like you otherwise will just end up parsing the file twice which isn't in anyone's best interest.

[sparr]

swc doesn't have all of the functionality of Bun.build