Include runtime and sdk version as a build output of source-build

[dseefeld]

This facilitates automation of package creation for distro maintainers.

cc @tmds

Related to #585

[omajid]

Does anyone have more context about this?

As a distro maintainer, I am okay with finding out the version from the tags that become available on github. It would be a nice-to-have if a build told me the SDK/ASP.NET/Runtime version at the end (in a structured, parseable format), but it's not a big deal (takes a few minutes a month).

I am guessing there are other benefits that I am missing. @tmds @crummel do you see any other use-cases/benefits of implementing this that make this more of a priority?

[crummel]

This is a prerequisite for a couple other items we have in mind - #747, #1610, and #2128 are the ones I can think of. I don't think it's urgent, but it's small, can be done now, and enables other scenarios, so that's why I put it in the first pass of automation improvements.

[omajid]

Thanks.

Do we need the versions to show up in a file or in the console/log? Or both?

[crummel]

I think a file since we'll want to use these in different CI steps, possibly even multiple files for ease of use - something like artifacts/build-info/{Runtime,Sdk,AspNet}Version.txt with just a single line each. Then in the YAML we can do something like

tarballName=dotnet-$(`cat RuntimeVersion.txt`)-$(`cat SdkVersion.txt`)

(a bit iffy on the syntax but it's something like that). @dseefeld @MichaelSimons any thoughts?