Strip noisy `.test.ts` suffixes from file names in test explorer tree

Clear and concise description of the problem

The test explorer shows test files as the literal file name, e.g. user.test.ts, which results in a lot of visual noise I have to ignore.

I would like an option to strip the .test.ts suffix, leaving just user. I'd be happy to implement and PR!

Suggested solution

Add a setting to the Vitest extension to remove file suffixes. We'd also need to support different test conventions, like .test.js, .spec.ts, etc.

Alternative

I imagine some people will still prefer having the explicit suffix to reflect the file system, so we should disable stripping by default, leaving it opt-in only?

Additional context

Validations

• Follow our Code of Conduct
• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.

Start by locating the test explorer tree's file-name rendering and the extension settings that control its display. Review how test file conventions are represented, including .test.js, .test.ts, and .spec.ts. Done means an opt-in setting strips the selected suffixes while leaving the explicit file names unchanged by default.