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

[cspotcode]

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?