[Hosts][EnvVar][RegPreview]improve nuget packages

[jaimecbernardo]

Summary of the Pull Request

Improves the nuget structure for the abstracted utilities:

• Add missing metadata to the packages.
• Build for any CPU, so the nuget packages can be used for any architecture.
• Remove the WinUIEx from the UI libraries, since it's unneeded. (It's only used by the app that consumes the libraries in our case).
• Remove the xbf files, which are unneeded.
• Release CI packs and signs the nuget packages.

PR Checklist

• References: Add some PowerToys utilities devhome#2072
• Communication: I've discussed this with core contributors already. If 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 for new binaries
  • WXS for installer for new binaries and localization folder
  • YML for CI pipeline for new test projects
  • YML for signed pipeline
• Documentation updated: If checked, please file a pull request on our docs repo and link it here: #xxx

Validation Steps Performed

Built the nugetpackages in CI, and changed our apps to use the nuget packages instead of the project reference to the UILibs. Built local installer this way and verified the Hosts, RegPreview and EnvVars utility still work.

[jaimecbernardo]

Hi @DHowett ,
I've stolen this from Terminal for signing nuget packages: 4adde1e
LGTY? 😉

[jaimecbernardo]

Packages used for testing are from this release pipeline:
https://microsoft.visualstudio.com/Dart/_build/results?buildId=97680319&view=artifacts&pathAsName=false&type=publishedArtifacts

[DHowett]

The signing stuff looks right to me! Thanks!