Improve Linux-on-Windows support

ALE supports running on Linux, BSD, and Mac OSX using Unix tools, and running on Windows using Windows tools. ALE does not currently support mixing Windows tools with Linux tools on Windows. A few issues have been raised about these types of issues, so it makes sense to collect those issue and discuss solutions here. Note that "support" is distinct from "might happen to work."

Right off the bat, ALE will probably never extend explicit support for cygwin. The cygwin rules for mixing Unix and Windows paths are difficult to handle and confusing, and I strongly believe that cygwin will fade into irrelevance as [Windows Subsystem for Linux ](https://docs.microsoft.com/en-us/windows/wsl/about) takes off. I won't go out of my way to break ALE running in Vim in cygwin, but I won't make any effort to fix it either.

MSYS support can be put down as a "maybe." If a small series of changes could be made somewhere to make it possible to run ALE more easily using MSYS tools, those changes can be considered.

Primarily, ALE should attempt to offer better support when Vim is run as a "Linux" program via the Windows Subsystem for Linux support in Windows. This is likely to increasingly become a common way to run Vim on Windows, so the support will matter more and more.

I still recommend installing GVim via the official installer on Windows, personally.

## Related Issues

* [#3359](https://github.com/dense-analysis/ale/issues/3359) Ale Fixers not loading for TSX files in WSL