Add DSC v3 resource discovery support in PowerToys with subfolder structure and PATH configuration (#43253)

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fix/what does it change/how was it tested (even manually, if necessary)?
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## Summary of the Pull Request

- Use DSCModules subfolder for JSON manifest files
- Use relative path "..\PowerToys.DSC.exe" in JSON manifests
- Configure PATH environment variable to point to DSCModules subfolder

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## PR Checklist

- [ ] Closes: #xxx
- [ ] **Communication:** I've discussed this with core contributors
already. If the work hasn't been agreed, this work might be rejected
- [ ] **Tests:** Added/updated and all pass
- [ ] **Localization:** All end-user-facing strings can be localized
- [ ] **Dev docs:** Added/updated
- [ ] **New binaries:** Added on the required places
- [ ] [JSON for
signing](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ESRPSigning_core.json)
for new binaries
- [ ] [WXS for
installer](https://github.com/microsoft/PowerToys/blob/main/installer/PowerToysSetup/Product.wxs)
for new binaries and localization folder
- [ ] [YML for CI
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/ci/templates/build-powertoys-steps.yml)
for new test projects
- [ ] [YML for signed
pipeline](https://github.com/microsoft/PowerToys/blob/main/.pipelines/release.yml)
- [ ] **Documentation updated:** If checked, please file a pull request
on [our docs
repo](https://github.com/MicrosoftDocs/windows-uwp/tree/docs/hub/powertoys)
and link it here: #xxx

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or any additional comments/features here -->
## Detailed Description of the Pull Request / Additional comments

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wherever possible, but list manual validation steps taken as well -->
## Validation Steps Performed

.pipelines/generateDscManifests.ps1

@@ -65,21 +65,28 @@ if (-not (Test-Path $outputDir)) {
     New-Item -Path $outputDir -ItemType Directory -Force | Out-Null
 }
 
-Write-Host "DSC manifests will be generated to: '$outputDir'"
+# DSC v3 manifests go to DSCModules subfolder
+$dscOutputDir = Join-Path $outputDir 'DSCModules'
+if (-not (Test-Path $dscOutputDir)) {
+    Write-Host "Creating DSCModules subfolder at '$dscOutputDir'."
+    New-Item -Path $dscOutputDir -ItemType Directory -Force | Out-Null
+}
 
-Write-Host "Cleaning previously generated DSC manifest files from '$outputDir'."
-Get-ChildItem -Path $outputDir -Filter 'microsoft.powertoys.*.settings.dsc.resource.json' -ErrorAction SilentlyContinue | Remove-Item -Force
+Write-Host "DSC manifests will be generated to: '$dscOutputDir'"
 
-$arguments = @('manifest', '--resource', 'settings', '--outputDir', $outputDir)
+Write-Host "Cleaning previously generated DSC manifest files from '$dscOutputDir'."
+Get-ChildItem -Path $dscOutputDir -Filter 'microsoft.powertoys.*.settings.dsc.resource.json' -ErrorAction SilentlyContinue | Remove-Item -Force
+
+$arguments = @('manifest', '--resource', 'settings', '--outputDir', $dscOutputDir)
 Write-Host "Invoking DSC manifest generator: '$exePath' $($arguments -join ' ')"
 & $exePath @arguments
 if ($LASTEXITCODE -ne 0) {
     throw "PowerToys.DSC.exe exited with code $LASTEXITCODE"
 }
 
-$generatedFiles = Get-ChildItem -Path $outputDir -Filter 'microsoft.powertoys.*.settings.dsc.resource.json' -ErrorAction Stop
+$generatedFiles = Get-ChildItem -Path $dscOutputDir -Filter 'microsoft.powertoys.*.settings.dsc.resource.json' -ErrorAction Stop
 if ($generatedFiles.Count -eq 0) {
-    throw "No DSC manifest files were generated in '$outputDir'."
+    throw "No DSC manifest files were generated in '$dscOutputDir'."
 }
 
 Write-Host "Generated $($generatedFiles.Count) DSC manifest file(s):"