Update wxs for WiX 5

[mhsmith]

Related PRs:

• Update to WiX 5 briefcase#2355
• Update wxs for WiX 5 briefcase-windows-app-template#14
  • The "app" PR contains the commit history of the files that are shared by both templates, so let's keep any discussion of those files there.

briefcase-repo: https://github.com/mhsmith/briefcase.git
briefcase-ref: wix4

PR Checklist:

• All new features have been tested
• All new features have been documented
• I have read the CONTRIBUTING.md file
• I will abide by the code of conduct

[freakboy3742]

As noted on beeware/briefcase-windows-app-template#14, this all makes sense, and works as advertised in my testing.