Add Windows batch scripts for JAR and WASM target

[ghost]

These are bash scripts: https://github.com/titzer/virgil/tree/master/bin

Running them on Windows requires a POSIX Shell like Cygwin or MSYS2.

I know Windows is not even supported, but the JAR and WASM target do work on Windows.

Having Windows batch scripts the users don't have to install any POSIX Shells.

[titzer]

I'm fine with having batch files for Windows. I don't primarily develop on Windows, so someone would have to write them and test them. I found this, which may make it possible that these scripts can run on both platforms.