chore: extract DEFAULT_DEV_PORT and DEFAULT_PREVIEW_PORT

[chenfan0]

Description

In the packages/vite/src/node/server/index.ts file, 5173 is used 3 times, and I personally think that 5173 should be extracted as a constant

What is the purpose of this pull request?

• Bug fix
• New Feature
• Documentation update
• Other

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[Shinigami92]

Maybe we also need to re-export it from https://github.com/vitejs/vite/blob/main/packages/vite/src/node/index.ts to make it available outside (via import ... from 'vite'), do we?

[chenfan0]

Maybe we also need to re-export it from https://github.com/vitejs/vite/blob/main/packages/vite/src/node/index.ts to make it available outside (via import ... from 'vite'), do we?

/packages/vite/src/node/index.ts file will export packages/vite/src/node/publicUtils.ts. so it can be accessed externally(via import ... from 'vite')