fix(cli): 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/cli.ts

@@ -169,7 +169,9 @@ cli
     '--force',
     `[boolean] force the optimizer to ignore the cache and re-bundle`,
   )
-  .option('--watchStdin', `[boolean] watch stdin and exit on EOF`)
+  .option('--watchStdin', `[boolean] watch stdin and exit on EOF`, {
+    default: !process.stdin.isTTY,
+  })
   .action(async (root: string, options: ServerOptions & GlobalCLIOptions) => {
     filterDuplicateOptions(options)
     // output structure is preserved even after bundling so require()
@@ -365,7 +367,9 @@ cli
   .option('--strictPort', `[boolean] exit if specified port is already in use`)
   .option('--open [path]', `[boolean | string] open browser on startup`)
   .option('--outDir <dir>', `[string] output directory (default: dist)`)
-  .option('--watchStdin', `[boolean] watch stdin and exit on EOF`)
+  .option('--watchStdin', `[boolean] watch stdin and exit on EOF`, {
+    default: !process.stdin.isTTY,
+  })
   .action(
     async (
       root: string,