pipeline template converter improvements

[scbedd]

Discovered over the course of completion of #7647.

• Auto-add @self to template references in stage template files (@scbedd)
• See if we can fix ordering (so variables goes above jobs), but without having to declare inner types for everything (otherwise we could use the order attribute in yamldotnet)
• Preserve multi-line powershell arguments with yaml > operator (@benbp)
• Figure out pool refactor as separate task
• Complete publish template in eng/common
• Simplify publish and just use PublishPipelineArtifact for everything (remove PublishType) instead PublishBuildArtifact. Use inline replace for nuget instead of common template (@benbp)
• Identify issue with eng/common/pipelines/templates/steps/publish-artifact.yml, the tool entirely deletes the content.
• Inject full necessary sdl configuration
• Modify eng/common/pipelines/templates/steps/publish-artifact.yml to properly handle individual files by placing said file in a separate folder before uploading that folder.
  • Just doing this in steps before the artifact publish attempt.