docs(swc): add vitest alias resolution configuration

[mag123c]

PR Checklist

Please check if your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/nestjs/docs.nestjs.com/blob/master/CONTRIBUTING.md

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Docs
• Other... Please describe:

What is the current behavior?

Vitest does not automatically resolve TypeScript path aliases (src/), unlike Jest, which uses moduleNameMapper.
This can lead to dependency resolution errors when running tests

Issue Number: nestjs/nest#14653

What is the new behavior?

• Updated the SWC documentation to include a fix for Vitest path alias resolution.
• Added resolve.alias configuration in vitest.config.ts to ensure correct module resolution.
• Explained why Vitest requires explicit path alias configuration, improving clarity for users.
• Ensured consistency with Jest’s moduleNameMapper behavior.

Does this PR introduce a breaking change?

• Yes
• No

Other information

This PR improves the official documentation by adding an alias resolution configuration to prevent common Vitest issues when running tests in NestJS projects. This ensures a smoother developer experience and avoids dependency resolution errors.

[kamilmysliwiec]

LGTM