Automatically taint when reporting errors from ItemCtxt This isn't very robust yet, as you need to use `itemctxt.dcx()` instead of `tcx.dcx()` for it to take effect, but it's at least more convenient than sprinkling `set_tainted_by_errors` calls in individual places. based on https://github.com/rust-lang/rust/pull/127357 r? `@fmease`