fix #2230 - prevent babel helpers duplication and condense bundle & types

[levimichael]

• Fixes ESM output contains many duplicated helpers #2230, by condensing the ESM bundle into a single file
• Usesrollup-plugin-dts to merge the types into one index.d.ts file
• Uses @rollup/plugin instead of manually passing the bundle to Babel post-build, and replaces rollup-plugin-babel usage

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[8bittitan]

If we are taking the time to update these, what do you think about moving to something like tsup overall? https://tsup.egoist.dev/

[8bittitan]

Should we also do this for the docsearch-js implementation as well?

[levimichael]

If we are taking the time to update these, what do you think about moving to something like tsup overall? https://tsup.egoist.dev/

Interesting idea, I'm not sure its worth the effort currently to swap out the bundler. We can revisit this in another PR!

[levimichael]

Should we also do this for the docsearch-js implementation as well?

Updated!