Add support for vim Operator::AddSurrounds.target in keymap config

[mgsloan]

cc @ConradIrwin. Found this while doing the keymap json schemas change. Does it make sense?

Release Notes:

• N/A

[ConradIrwin]

I don't think this is needed, but it's also doesn't seem like it would cause any problems.

In typical vim fashion you first hit a binding (ys by default) to push AddSurrounds to the operator stack, and then you hit a binding ("a" or "i") to push the Around/Inside operator to the stack; and finally you hit another key binding . This causes (convolutedly) the AddSurrounds operator to be popped and a new one to be pushed with the target object.

If someone wanted to bind a specific key to "add-surrounds to a specific object" the vim approach would be to use workspace::SendKeystrokes: ["y s a w"] instead of constructing the object manually.