[Search Documents] base64 > strings can roundtrip failing in nightly runs

[jerryshia]

Search Documents nightly test runs are failing with:

Error message:
Buffer is not defined

Stack trace:
ReferenceError: Buffer is not defined
❯ encode dist-test/browser/src/base64.js:9:2
❯ dist-test/browser/test/internal/base64.spec.js:9:20

For more details check here:
https://dev.azure.com/azure-sdk/internal/_build/results?buildId=4423242&view=results

[jeremymeng]

This is due to failure in building browser tests which prevented proper replacing of browser version of code files.

The build error is tracked by #29283