fix(vite): default watchStdin to !process.stdin.isTTY

Fixes the issue with running Vite under Elixir and doesn't cause issues
when running Vite programmatically [1]

[1] #4079

packages/vite/src/node/server/index.ts

@@ -1036,7 +1036,7 @@ export const serverConfigDefaults = Object.freeze({
   host: 'localhost',
   https: undefined,
   open: false,
-  watchStdin: false,
+  watchStdin: !process.stdin.isTTY,
   proxy: undefined,
   cors: true,
   headers: {},