Use powershell script to flatten ESRP release folder (Azure#35093)

* Use powershell script to flatten ESRP release folder
* Skip maven-metadata.xml.* files when flattening ESRP package folders

eng/pipelines/templates/steps/java-publishing.yml

@@ -97,6 +97,15 @@ steps:
           -ArtifactIDFilter "${{ parameters.ArtifactID }}"
           -GPGExecutablePath ${{ parameters.GPGExecutablePath }}
           -InformationAction Continue
+    - task: PowerShell@2
+      displayName: 'Flatten output folder'
+      inputs:
+        pwsh: true
+        workingDirectory: $(Agent.BuildDirectory)
+        filePath: ${{ parameters.JavaRepoRoot }}/eng/scripts/Flatten-MavenPackageFolder.ps1
+        arguments: >
+          -Path ${{ parameters.OutputDirectory }}
+          -InformationAction Continue
     - ${{if and(eq(parameters.ShouldPublish, 'true'), ne(parameters.StageOnly, 'true'))}}:
       - task: EsrpRelease@2
         displayName: 'Publish to ESRP'

eng/scripts/Flatten-MavenPackageFolder.ps1

@@ -0,0 +1,45 @@
+#Requires -Version 7
+param(
+  [Parameter(Mandatory=$true)][string]$Path
+)
+
+Set-StrictMode -Version 2.0
+
+$ErrorActionPreference = "Stop"
+
+$files = Get-ChildItem -Path $Path -Recurse -File -Force -ErrorAction Stop
+
+$paths = @{}
+
+foreach($file in $files) {
+    $name = $file.Name
+
+    # Skip maven-metadata.xml files. These are generated for each package and are not needed by ESRP.
+    if($name -match "^maven-metadata\.xml(\..*)?$") {
+        continue
+    }
+
+    if($paths.Keys -contains $name) {
+        Write-Error "Duplicate file name: $name`n  $($paths[$name]) and $($file.FullName)"
+        Write-Error "Unable to flatten: $Path"
+        exit 1
+    }
+
+    $paths[$name] = $file.FullName
+}
+
+# Move the files to the root of the directory.
+foreach($name in $paths.Keys) {
+    $oldPath = $paths[$name]
+    $newPath = Join-Path -Path $Path -ChildPath $name
+    Move-Item -Path $oldPath -Destination $newPath -Force -ErrorAction Stop
+}
+
+$dirs = Get-ChildItem -Path $Path -Directory -Force -ErrorAction Stop
+
+# Remove all child directories.
+foreach($dir in $dirs) {
+    Remove-Item $dir.FullName -Force -Recurse -ErrorAction Stop
+}
+
+exit 0