The existing tests for transform_view::iterator weren't quite right, and can be simplified now that we have more of C++20 available to us. Having done that, let's use the same pattern for iota_view::iterator as well.
The transform_view test had been commented out because we were missing std::is_eq (D110515). However, it turned out that the commented-out test was a bit bogus for a couple other reasons:
- it lacked coverage for the rewritten operators and operator==
- it was a bit overcomplicated (especially now that std::views::transform has landed)
- it wrongly assumed that the ContiguousView from "types.h" had non-three-way-comparable iterators
Note the design decision here to rely on the fact that (for now) random_access_iterator has no operator<=>. If we ever add one, this test's sanity-check will fail, and we'll have to go find a different legacy iterator to use instead.