Community Toolkit upgrade to 8.1.240821 (after .84 is verified stable)

[crutkas]

Summary of the Pull Request

Upgrade of the WinUI Toolkit. This will upgrade the target .net framework as well as a requirement for Toolkit

Reviewer notes:

1. Things to note that i found odd, WorkspacesLib.vcxproj required me to add in CppWinRT for some reason.

Moving parts:

This is one of 4 major upgrades we need to accomplish for AoT for WinUI.

1. CsWinRT 2.1.1<- Draft PR Community Toolkit upgrade to 8.1.240821 (after .84 is verified stable) #34419
2. WinAppSDK 1.6<- Draft PR Community Toolkit upgrade to 8.1.240821 (after .84 is verified stable) #34419
3. Toolkit <- this PR

Bonus points:

1. Vcxproj prop abstraction for WinAppSdk
2. CppWinRT

PR Checklist

• Closes: #xxx
• 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

Detailed Description of the Pull Request / Additional comments

Validation Steps Performed

[crutkas]

/azp run

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[crutkas]

testing against dart

[crutkas]

crap, looks like the merge broke stuff

[jaimecbernardo]

Did a all around test from the Dart binaries. LGTM! Code changes look good as well. Thank you!