swift codegen: Add operation name to generated operation

[js]

This adds operationName to the generated swift declarations.

It goes together with this PR in apollo-ios, but should not be dependent on each other

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

[js]

Not a JS dev so not quite clear to me why some of the tests are failing in CI? Locally npm test only gives me an error for the Git integration › Returns commit, branch, message, committer, and remoteUrl test, since I have a different remote

[js]

The failing apollo-tooling test says Type check failed. Run 'npm run client:codegen' in the output, but seems I need an API key to do that (when I run it locally): { Error: Error in "Loading schema for engine": Error: ENGINE_API_KEY not found

Really want to get this change in :)

[js]

Rebased against master, still seem to get test failures in CI (but not locally) on unrelated things. Are the tests expected to be flaky?

[designatednerd]

Swift stuff looks good - I'd appreciate a look from someone who knows TypeScript though!

[trevor-scheer]

This was just resolved in #1386, apologies that I didn't get to this first and sooner. Feel free to reopen if I've overlooked anything.