[libc++] [test] Test that list::swap/move/move-assign does not invalidate iterators.

And remove the dedicated debug-iterator test; we want to test this in all modes.
We have a CI step for testing the whole test suite with `--debug_level=1` now.

Part of https://reviews.llvm.org/D102003

GitOrigin-RevId: 8935c8449b7b17049990d29443ed29dde315f281
4 files changed