[api-extractor] Will strip `declare var` content after rollup types

[qmhc]

Summary

https://stackblitz.com/edit/vitejs-vite-ldof7q7z?file=package.json

Repro steps

Run pnpm run build, then check the declaration file under dist.

Expected result: No type error.

Actual result: Get an error Cannot find name 'obj'.

Details

Will be correct if change var to let.

Standard questions

Please answer these questions to help us investigate your issue more quickly:

Question	Answer
@microsoft/api-extractor version?	7.51.1
Operating system?	Linux
API Extractor scenario?	rollups
Would you consider contributing a PR?	No
TypeScript compiler version?	5.7.2
Node.js version (node -v)?	18.20.3