fix: Replace all backslashes when normalizing path in getFormattedDia…

…gnostic (#17915)

I have not bumped into any bug, I was just playing around https://lgtm.com/projects/g/vercel/next.js/, and this looked like a legit suggestion to fix

packages/next/lib/typescript/diagnosticFormatter.ts

@@ -45,7 +45,7 @@ export async function getFormattedDiagnostic(
     const character = pos.character + 1
 
     let fileName = path.posix.normalize(
-      path.relative(baseDir, diagnostic.file.fileName).replace(/\\/, '/')
+      path.relative(baseDir, diagnostic.file.fileName).replace(/\\/g, '/')
     )
     if (!fileName.startsWith('.')) {
       fileName = './' + fileName