[Swift Codegen] Adding some explicit type annotations

[djs-code]

Adding explicit type annotations for operationDefinition, operationName, and possibleTypes to help out Swift compile times.

TODO:

• Update CHANGELOG.md* with your change (include reference to issue & this PR)
• Make sure all of the significant new logic is covered by tests
• Rebase your changes on master so that they can be merged easily
• Make sure all tests and linter rules pass

[apollo-cla]

@djs-code: Thank you for submitting a pull request! Before we can merge it, you'll need to sign the Apollo Contributor License Agreement here: https://contribute.apollographql.com/

[designatednerd]

@djs-code out of curiosity, what's the compile time improvement you're seeing after adding explicit types?

[designatednerd]

looks like something in here is failing the linter - @trevorblades or @abernix any rough clue what?

[djs-code]

@designatednerd The benchmarking wasn't too extensive, but the handful of files I tested the before/after of yielded a 12~15% improvement.

[designatednerd]

That's not bad for just throwing in a few types.

Let's see what the JS group have to say when they have a moment about the lint failures, I already kicked the build once and am seeing the same issues - you might be able to trigger the linter to auto-format by saving and running tests with npm test before committing, but that's been suuuuper inconsistent for me.

[designatednerd]

Apparently: “Running npm run lint-fix will apply those changes.”

_{Sent with GitHawk}

[djs-code]

@designatednerd Looks like that did the trick! 🎉

[djs-code]

...or did I speak too soon? 🤔

[designatednerd]

OK kicked the build - the thing that failed won't rerun until after all the other tests are done

[designatednerd]

Good to merge whenever CI gets its shit together

[designatednerd]

Tooling team's on it - your code is fine. 😃

[djs-code]

@designatednerd Heya, have we been able to nail down what's going awry here?

[designatednerd]

@djs-code Can you try rebasing off master? I believe it may have been fixed there

[djs-code]

@designatednerd Yup, looks like we're good to go. 👍