Make type-naming scheme a bit smarter

For example if you have a field `doThing: DoThingMutation` or `error: MyError` we should be able to be a bit smarter than `DoThingDoThingMutation`/`ErrorMyError`, in the same way we currently shorten `error: Error` to just `Error`. Although of course get too fancy here, and it gets hard to think about, and too magical.

The issue names no files or tests; start by locating the type-naming logic and the existing special case that shortens `error: Error` to `Error`. Define a narrowly scoped rule covering the provided examples, add tests for those cases, and ensure unrelated names are not made overly magical.

Written by the indexing model from the issue text.