Introduce ExcludeFromDotNetBuild control

[mmitche]

See https://microsoft-my.sharepoint.com/:w:/p/mmitche/EdchH8A4okpOoKhkki1sJEYB0LyAaaCyX5_6A887gL744Q?e=JERvht for full design:

When “true” and DotNetBuild == “true”, the project is not built.
This is equivalent to ExcludeFromBuild being set to true when DotNetBuild == “true”.
This control applies to project properties.

See locations where ExcludeFromVerticalBuild/SourceBuild exist today.

[dotnet-issue-labeler]

I couldn't figure out the best area label to add to this issue. If you have write-permissions please help me learn by adding exactly one area label.

[mmitche]

Completed.