fix: add all MTG packages to generated nuget.config for OAI regenpreview (#9124)

The regen preview script is failing locally now do to the other MTG
nuget packages not being found in the upstream feed when it should be
looking at the local disk feed. Also addresses some issues with npm
caching when regenerating OAI locally.

Author: jorgerangel-msft

packages/http-client-csharp/eng/scripts/RegenPreview.psm1

@@ -516,7 +516,9 @@ function Update-OpenAIGenerator {
         -NuGetConfigPath $nugetConfigPath `
         -SourcePath $DebugFolder `
         -PackagePatterns @(
-            "Microsoft.TypeSpec.Generator.ClientModel"
+            "Microsoft.TypeSpec.Generator.ClientModel",
+            "Microsoft.TypeSpec.Generator.Input"
+            "Microsoft.TypeSpec.Generator"
         )
 
     # Update codegen/package.json
@@ -553,20 +555,20 @@ function Update-OpenAIGenerator {
         $packageJson | ConvertTo-Json -Depth 100 | Set-Content $codegenPackageJsonPath -Encoding UTF8
 
         # Delete package-lock.json to force regeneration with new dependencies
-        $packageLockPath = Join-Path $OpenAIRepoPath "codegen" "package-lock.json"
+        $packageLockPath = Join-Path $OpenAIRepoPath "package-lock.json"
         if (Test-Path $packageLockPath) {
-            Write-Host "Deleting codegen/package-lock.json..." -ForegroundColor Gray
+            Write-Host "Deleting package-lock.json..." -ForegroundColor Gray
             Remove-Item $packageLockPath -Force
         }
 
         # Run npm install to regenerate package-lock.json with local dependencies
-        Write-Host "Installing dependencies in codegen directory..." -ForegroundColor Gray
-        Push-Location (Join-Path $OpenAIRepoPath "codegen")
+        Write-Host "Installing dependencies in openai directory..." -ForegroundColor Gray
+        Push-Location $OpenAIRepoPath
         try {
-            $npmOutput = Invoke "npm install" (Join-Path $OpenAIRepoPath "codegen")
+            $npmOutput = Invoke "npm install" $OpenAIRepoPath
             if ($LASTEXITCODE -ne 0) {
                 Write-Host $npmOutput -ForegroundColor Red
-                throw "npm install failed in codegen directory"
+                throw "npm install failed"
             }
             Write-Host "  Dependencies installed" -ForegroundColor Green
         }