refactor(rsc): check module node type instead of extension

[hi-ogawa]

Description

• Closes Replace isCSSRequest check with moduleNode.type === 'css' #617

[hi-ogawa]

It looks like css is actually type: 'js' 🤔

EnvironmentModuleNode {
  environment: 'rsc',
  url: '/src/index.css',
  id: '/home/hiroshi/code/others/vite-plugin-react/packages/plugin-rsc/examples/starter/src/index.css',
  file: '/home/hiroshi/code/others/vite-plugin-react/packages/plugin-rsc/examples/starter/src/index.css',
  type: 'js',
  info: undefined,
  meta: undefined,
  importers: Set(1) {
    EnvironmentModuleNode {
      environment: 'rsc',
      url: '/src/root.tsx',
      id: '/home/hiroshi/code/others/vite-plugin-react/packages/plugin-rsc/examples/starter/src/root.tsx',
      file: '/home/hiroshi/code/others/vite-plugin-react/packages/plugin-rsc/examples/starter/src/root.tsx',
      type: 'js',

[hi-ogawa]

This is because type: 'css' is only for .css?direct request https://github.com/vitejs/vite/blob/95927d9c0ba1cb0b3bd8c900f039c099f8e29f90/packages/vite/src/node/server/moduleGraph.ts#L77

[hi-ogawa]

It looks like I misunderstood module type. type: 'css' is for .css?direct request which holds raw css text string instead of export default '...' string.