fn capture_all(&mut self, unique_symbol: UniqueSymbol) {
        for scope in self.scopes.iter_mut() {
            scope.nonlocals.push(unique_symbol);
        }
    }
Adds a symbol as a captured variable in all scopes.
Used in conjunction with `uncapture_all` to build
hoisting chains.
passerine/src/compiler/hoist.rs