Graduate swc out of experimental; add `swc: true` convenience option

The swc transpiler seems to be pretty stable now.  We can graduate it out of experimental and also add an `swc` option as an alias to using the swc transpiler.

* Remove `experimental` from the name
	* keep old name for backwards compatibility
* Add `swc: true` which enables the transpiler and transpile-only
* add `--swc` CLI flag?