add common helpers

helpers/clean-toolcache.ps1

@@ -0,0 +1,13 @@
+param (
+    [string] $ToolName
+)
+
+$targetPath = $env:AGENT_TOOLSDIRECTORY
+if ($ToolName) {
+    $targetPath = Join-Path $targetPath $ToolName
+}
+
+if (Test-Path $targetPath) {
+    Get-ChildItem -Path $targetPath -Recurse | Where-Object { $_.LinkType -eq "SymbolicLink" } | ForEach-Object { $_.Delete() }
+    Remove-Item -Path $targetPath -Recurse -Force
+}