Fix var binding to scope

[yassere]

The recent scope-tracking improvements changed the kind of scope that var bindings are attached to. This fixes the JSVariableDeclaration evaluator so that it can add var bindings to the scope.

It also changes JSVariableDeclarationStatement so that it doesn't attempt to add var bindings, because that should be handled by addVarBindings on the relevant block. Without this change, var declarations inside a nested block scope would cause an error to be thrown.

Closes #574
Closes #535

[sebmck]

I don't think this is correct because:

function foo() {
  {
    var bar;
  }
  bar;
}

The bar binding should be set on the function but I believe with this change it would be on the inner block.

[yassere]

I think that the bar var binding in your example is on the block scope that's the direct child of the function declaration, which is what I thought your intention was with the recent changes. It looks like addVarBindings in the JSBlockStatement evaluator is trying to add var bindings to the "block" scope, but nothing gets added because of this conditional. Sorry if I misunderstood.

If I use this branch to lint the sample:

function foo() {
  {
    var bar;
    let baz;
  }
  bar;
  let rome;
}

with the rule:

if (node.type === "JSBlockStatement") {
  console.log(scope.bindings);
}

I see that the rome and bar bindings are in the same scope and the baz binding is in a different scope by itself.

[sebmck]

Ah right. I can't really make a lot of sense of the existing code (that I wrote) so I took a look and rethought the whole var injection strategy. I'll have a PR in a minute.

[yassere]

Resolved by #589