[api-extractor] auto add `.api.md`

[0618]

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After version 7.40.1, started to generate new report files with .api.md.

Summary

In my config, I have "reportFileName": "API.md",, so it used to generate API.md for me.

However, with the new version, it ignores the old API.md, but started generates a API.md.api.md instead.

Repro steps

1. in api-extractor.json, set "reportFileName": "API.md",
2. run api-extractor

Expected result: Old version generates API.md

Actual result: New version generates API.md.api.md

Details

It might related to https://github.com/microsoft/rushstack/pull/4621

The new minor version upgrade should not contain any breaking change.

Standard questions

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

Question	Answer
@microsoft/api-extractor version?	7.40.1
Operating system?
API Extractor scenario?
Would you consider contributing a PR?	No.
TypeScript compiler version?	~5.2.0
Node.js version (node -v)?	v20.11.1