Allow environment variables inside "".

[certik]

This works:

~$ echo $PATH
C:\Program Files (x86)\Microsoft SDKs\Azure\CLI2\wbin;C:\Windows\system32;C:\Win...

This does not:

~$ echo "$PATH"

~$

The quotes are however needed for spaces to work (such as in Program Files) when assigning to a variable (such as appending to $PATH).

[certik]

Note that this works:

$ echo "$(uname)"
Windows_NT

So we do some substitutions, just not environment variables yet.