maven_install unusable on Windows due to hashbang in coursier executable

Trying to use a simple maven_install rule on windows (which works fine on mac) results in the following error:

`activity depends on @maven//:com_google_android_gms_play_services_nearby in repository @maven which failed to fetch. no such package
'@maven//': Unable to run coursier: java.io.IOException: ERROR: src/main/native/windows/process.cc(202): CreateProcessW("C:\users\kalma\_bazel_kalma\waikar5b\external\maven\coursier"): %1 is not a valid Win32 application.
(error: 193)`

This problem is obvious if you open the coursier binary it points to, as it is actually wrapped in a shell script, and starts with:
`#!/usr/bin/env sh
nargs=$#
`

Obviously on Windows this is not supported as a standard executable. I tried using different versions of rules_jvm_external and bazel itself to see if perhaps it worked historically, but it doesn't seem so.

Start at the maven_install entry point and the coursier executable named in the error; inspect how the shell-wrapped executable is launched on Windows. Reproduce the CreateProcessW failure with the sample dependency, then verify that the Windows invocation can fetch the Maven artifact successfully.

Written by the indexing model from the issue text.