Always generate checksums as last part of publish job

[wtgodbe]

My first iteration of publishing checksums for this repo didn't work, since it generated checksums for some assets, before those assets were signed (specifically the installer zips). Instead, I'm here trying to ensure that checksums are only generated once per build, after all build and signing jobs are done. I'm using the assumption that the step that passes _PublishArgs is always the final build step, and therefore we can safely hook the checksum target into AfterSigning.proj in that leg (note that only the winx64/x86 job has multiple build steps - all the other jobs just run build once & pass _PublishArgs to that).

This should generate checksums for the same set of assets as my previous solution.

Internal build: https://dev.azure.com/dnceng/internal/_build/results?buildId=581767

Resolves part of #18792 (still need to port this to master, and find another solution for 2.1)

[wtgodbe]

Project gets imported here: https://github.com/dotnet/arcade/blob/cc4af3898310cf2826d78de453dff4a25905b888/src/Microsoft.DotNet.Arcade.Sdk/tools/AfterSigning.proj#L29

[wtgodbe]

Initial build didn't work since AfterSigning.targets doesn't import root d.b.props, so it didn't have some properties I was expecting it to. New build: https://dev.azure.com/dnceng/internal/_build/results?buildId=581882

[wtgodbe]

Last build didn't work either, because AfterSigning.proj in Arcade doesn't import the Arcade SDK props/targets files. New build: https://dev.azure.com/dnceng/internal/_build/results?buildId=582051

[wtgodbe]

New build with a tailored list of extensions to generate checksums for: https://dev.azure.com/dnceng/internal/_build/results?buildId=582357

[mthalman]

I'm no expert on the product build side of things but things seem fine to me.

[wtgodbe]

Here's the set of checksums that got published - I'm working on verifying that they're valid. @dougbu @JunTaoLuo @mthalman any last concerns with the content of the PR, or the content of what it generated?

[dougbu]

A few nits and questions but only one "should fix". I don't need to review again though I am interested in the questions.

[wtgodbe]

I validated that the checksums are correct this time (w/ $(Get-FileHash <filepath> -Algorithm SHA512).Hash, but noticed that I missed the .rpm and .wixlib files. I'll add those.

[wtgodbe]

New build which should include wixlib/rpm checksums: https://dev.azure.com/dnceng/internal/_build/results?buildId=583841

[wtgodbe]

https://dev.azure.com/dnceng/internal/_build/results?buildId=584014

[wtgodbe]

Yarn endpoint exploded. I'll hit retry when I can

[JunTaoLuo]

One question but otherwise looks good.