Port shell scripts to PowerShell, merging w/ Batch scripts where possible

I've come around to the idea of PowerShell on Linux after getting a working Nix expression into the repo. After all, if I make Nix a requirement for Linux devs (as I plan to), what harm is another dependency?

Since c6270241f55b77a26dfb28c54a822b9269e47ec2, PowerShell is a soft builddep for BizHawk, and it will automatically installed with dotnet tool restore.

A note re: Git pre-commit hooks; apparently there's a new way to add those which makes using PowerShell simpler than the mess we ended up with, see PowerShell issue 16480.

If an OS-specific call needs to be made (considering all of the .NET BCL is available, unlikely) it may be easier to use a polyglot hack in a separate script than to conditionally invoke the relevant programs. I'm not familiar enough with PowerShell to say.

notes:

• set -x

It might be worth extracting shell scripts from the GitLab CI config and porting them as well. For the most part they just call the scripts in /Dist. (See also my notes on dotnet publish.)

If MSBuild can run PowerShell scripts (I haven't checked), we can replace everything in /Build and the target in BizHawk.Version.csproj with PowerShell too. Replaced w/ Source Generator.

see also #2073

Start by inventorying the shell scripts in /Dist and /Build, then inspect the shell fragments in the GitLab CI configuration and the target formerly mentioned in BizHawk.Version.csproj. Check the relationship to #2073 and the linked notes before defining the scope. Done means the agreed scripts and CI/build paths have PowerShell equivalents and continue to work across the supported environments.