Auto merge of #124393 - scottmcm:do-the-macros-still-matter, r=joboet

Convert some iter macros to normal functions

With all the MIR optimization changes that have happened since these were written, let's see if they still actually matter.

\*perf comes back\*

Well, it looks like it's not longer relevant for instruction, cycle, nor wall-time perf.  Looks like a bunch of things are maybe 10kb bigger in debug, but some are also 50k *smaller* in debug.

So I think they should switch to being normal functions as the "greatly improves performance" justification for them being macros seems to no longer be true -- probably thanks to us always building `core` with `-Z inline-mir` so the difference is negligible.

Author: bors