I'm starting on bringing up UWP support in flutter/plugins, and need the infra brought online for that:

• A recipe that looks like the existing Windows plugin recipe except:
  • It runs --enable-windows-uwp-desktop instead of --enable-windows-desktop
  • It passes --winuwp instead of --windows to script commands

Ideally it should be a separate stand-alone recipe so that we can see UWP failures separately from Win32 failures, but if we have to combine them that would be livable.

(I'll have a test PR available shortly to try running the new recipe against to see if it's working.)