High level problem: when I don't want tsup to build target > es2021, but do use emitDecoratorMetadata, I'm forced to opt-in to SWC transforms that break my legacy decorators.

See

Note that esbuild automatically detects the useDefineForClassFields tsconfig option. But SWC does not (automatically).

Two things:

1. Set the transform option like so https://swc.rs/docs/configuration/compilation#jsctransformusedefineforclassfields inferred via target or from the user's tsconfig
2. Set the target based on that of tsup config? I'm not sure if the hardcoded es2022 is intentional / for a reason (ie esbuild for down-level it better)

I'd be happy to try and do this in a PR