With the decision to wind down continued development of the Windows UWP embedder, we'll need to clean up existing work that has landed.

• Delete any UWP-related documentation from flutter.dev and the wiki.
• Remove UWP support from any codelabs, samples, etc.
• Remove UWP app support in the tool (template, logic, etc.)
• Eliminate UWP plugin support in the tool (template, logic, etc.)
• Eliminate UWP infra for flutter/plugins (e.g. [flutter_plugin_tool] Add support for building UWP plugins plugins#4047, [ci] Enable the new Windows targets plugins#4325)
• Disable building, testing, and uploading UWP artifacts on our engine bots
  • Eliminate Windows UWP Engine target from engine .ci.yaml.
  • Wait for the CI target change to roll to the flutter/infra repo.
  • Delete UWP support from engine recipe
• Eliminate UWP support from the gn wrapper
• Delete UWP embedder source/build files. Close any TODO-related bugs that appear in that code that don't also appear elsewhere.