Get-PR-Diff.ps1 excludes deletes from ChangedServices

If you delete a file from an sdk/ directory, that service directory isn't included in ChangedServices:
https://github.com/Azure/azure-sdk-tools/blob/main/eng/common/scripts/Generate-PR-Diff.ps1#L75

```json
{
"ChangedFiles": [
"sdk/automation/Azure.ResourceManager.Automation/src/Customized/AutomationCertificateData.cs"
],
"ChangedServices": [
"automation"
],
"ExcludePaths": [],
"DeletedFiles": "sdk/appconfiguration/Azure.Data.AppConfiguration/src/ConfigurationClient.cs",
"PRNumber": "-1"
}
```

I think a reasonable user would consider `appconfiguration` a changed service.

Start in eng/common/scripts/Generate-PR-Diff.ps1 around line 75 and inspect how deleted files are handled when building ChangedServices. Reproduce the example with a deleted file under sdk/appconfiguration, then verify that appconfiguration appears in ChangedServices while the existing output remains correct.

Written by the indexing model from the issue text.