Targeting Pack common infrastructure

[dleeapho]

[dagood] https://github.com/dotnet/core-setup/pull/5085#discussion_r253991314 has some thoughts on handling packs similar to runtime.<rid>.<package id> packages using the .builds infra. Fewer dirs and files that way, maybe more maintainable and easily usable in other repos. (Or replace the infra completely with something simpler.)

List of refactoring ideas from earlier PRs to improve this:

https://github.com/dotnet/core-setup/pull/5114

• Remove generatemsi.ps1 powershell scripts, use msbuild projects with shared targets.
  • Peek at wixproj, but likely stick with Execs for now.
• Consider unifying targeting pack installer creation with targeting pack pkgproj. This could make the targeting pack creation entry point cleaner.
  • I also want to look into merging Microsoft.NETCore.App.Ref.pkgproj into Microsoft.NETCore.App.pkgproj, and using it to drive other packs (Runtime, AppHost) as well. Same goal: cleaner entry point.
• Share WiX project files to avoid boilerplate.

• Another thing to consider is inserting a layout phase between collecting assets and pack. That way the content of the pack can be defined by the layout instead of vice-versa.

[dagood]

Closing: this was made common enough that we were able to split off dotnet/windowsdesktop for 5.0. Making an improved version (to make it more reasonable to onboard new repos) is tracked at https://github.com/dotnet/arcade/issues/2704.