Allow running devenv commands from the context of a selected VS

[kzu]

It's useful to be able to run some built-in commands, like devenv -updateconfiguration or devenv -rootSuffix Exp.

The proposed syntax after talking with @adalon is:

 vs [nickname] [options]

Examples:

vs master --updateConfiguration  => Start master dev cmd prompt & execute devenv -updateConfiguration
vs master c:\code\foo.sln

One useful option that could be alias for devenv.exe is:

--exp  => devenv.exe /rootSuffix Exp

We should likely document in -?|h|help the built-in arguments too.

@adalon mentioned that "It should run the specified devenv command using the associated prompt context (VsDevCmd.bat)."
I don't think that should be necessary since it's not necessary to run devenv.exe with parameters itself from a developer command
prompt. So just running it with the provided args would be just fine I think.

[kzu]

This is mostly already covered with the existing vs run which is the default command, so vs also runs devenv.exe. The alias for --exp would be useful.

[kzu]

I considered this covered by the existing vs run support plus 0d8059c