Re-order builds table

[richlander]

The builds table has an undiscernible order.

https://github.com/dotnet/installer#build-status

The most obvious order is OS than arch, or the opposite. Example: https://hub.docker.com/_/microsoft-dotnet-sdk/

[dagood]

There's some platform order fixup in a similar table in dotnet/runtime being suggested in this PR: dotnet/runtime#43392. Might be good to follow the same pattern.

[richlander]

Yes. One pattern for all repos, please.