Migrate to ESM only

[43081j]

We currently ship UMD, CJS and ESM.

Each of these also ships a sourcemap.

Suggestion:

• ESM only (drop UMD, CJS)
• Drop sourcemaps (published code is already readable)

Happy to do the PR if you're open to it

[sxzz]

relate to #301 (comment)

[sxzz]

I'm cooking it https://github.com/sxzz/magic-string/tree/feat/ts-esm

[43081j]

FYI @antfu we still ship source maps in Kevin's change. I think we should turn that off and make sure introducing tsdown didn't add minification

[sxzz]

@43081j I agree. However, I enabled source maps because the previous code already included them, and the bundle didn’t apply any code transformations, such as minification.

We could consider removing it in the next minor release, provided Anthony has no objections.

[43081j]

I'm not too concerned with why they were enabled in the pr or before. Just saying we should now turn them off either way.

Happy to make the pr if you don't have the time