Using node instead of getNode()

[Janther]

it has a cleaner type for the type checks, and the standard in prettier's parsers.
using the same approach, getNode(2) was replaced by grandparent.
I also added some really quick refactors that I found when replacing these cases and don't really merit another PR.

[fvictorio]

I don't agree with some of the refactors here (e.g., I think destructuring + aliases like const { foo: bar } = qux are generally less readable than const bar = qux.foo), but since this is mostly a personal preference, I'm ok with merging this PR as is.

[Janther]

happy to review these destructures in most cases I use the alias in a function signature where I don't have access to the = and renaming everything to the property name would look weird:

function printComment({ node: comment }) {
  if (isComment(comment)) {
    return comment.print();
  }

  throw new Error(`Not a comment: ${JSON.stringify(comment)}`);
}

And the other place where I use the alias is in a for...of loops with a similar reason.

    for (const { variant: attribute } of this.attributes.items) {
      if (
        typeof attribute !== 'string' &&
        attribute.kind === NonterminalKind.ModifierInvocation
      ) {
        attribute.cleanModifierInvocationArguments();
      }
    }