Next.js doesn't support Typescript file configuration for postcss

[coderrshyam]

Link to the code that reproduces this issue

https://codesandbox.io/p/sandbox/github/vercel/next.js/tree/canary/examples/reproduction-template

To Reproduce

1. Rename postcss.config.mjs to postcss.config.ts
2. Run npm run dev

Current vs. Expected behavior

Current Behavior
The page doesn't have any style looking like page without css.

Expected Behavior
It should compile all css corectly without any issue and the page have styles.

Provide environment information

Operating System:
  Platform: win32
  Arch: x64
  Version: Windows 11 Home Single Language
  Available memory (MB): 16069
  Available CPU cores: 12
Binaries:
  Node: 22.15.0
  npm: 11.3.0
  Yarn: N/A
  pnpm: 10.10.0
Relevant Packages:
  next: 15.3.2 // Latest available version is detected (15.3.2).
  eslint-config-next: 15.3.2
  react: 19.1.0
  react-dom: 19.1.0
  typescript: 5.8.3
Next.js Config:
  output: N/A

Which area(s) are affected? (Select all that apply)

CSS

Which stage(s) are affected? (Select all that apply)

next dev (local), next build (local), next start (local), Vercel (Deployed), Other (Deployed)

Additional context

Support typescript for postcss.

Typescript for all and everywhere :)