Support to subsystem commands

[leonardovilarinho]

• VSCode Version: 1.18.1
• OS Version: Windows 10

Steps to Reproduce:

1. Change git.path to bash -c git or similar.
2. Restart VSCode
3. Try execute anywhere action with Git.

We can define an flag to comunication with wsl, e.g. git.path: "bash -c 'git ${args}'".

With it call `bash -c 'git log' command for example.

It can use whit npm, pyhton, npm, anywhere commands.

Reproduces without extensions: No

[joaomoreno]

#9502