And not just called to be listed.
This was a major performance hang when repeatedly switching back-and-forth between a large `include!`d file (but there are others)..
More correctly, *also* per-token. Because as it turns out, while the top-level edition affects parsing (I think), the per-token edition affects escaping of identifiers/keywords.
It should be left biased, not right biased, because when e.g. the use has typed `h` then requested completion, the `h` is what we want to find, not the next token (which might indeed be inside a macro call).
I'm not sure why I wrote `right_biased()` to begin with (I remember I had a reason and not just "both should work"), I might've copied the code in `expand_and_analyze()` (which is wrong, because there it lookups on the speculative file, where right biased will always find the correct token and left biased not).
This is still not perfect, because there might not be an identifier already typed then we might still end up in a macro call, but this is the best we can do.
We should immediately mark them as finished, on the first entry.
The funny (or sad) part was that this bug was pre-existing, but previously to #18327, it was causing us to generate bindings non-stop, 65535 of them, until we get to the hardcoded repetition limit, and then throw it all away. And it was so Blazingly Fast that nobody noticed.
With #18327 however, this is still what happens, except that now instead of *merging* the fragments into the result, we write them on-demand. Meaning that when we hit the limit, we've already written all previous entries. This is a minor change, I thought for myself when I was writing this, and it's actually for the better, so who cares. Minor change? Not so fast. This caused us to emit 65535 repetitions, all of which the MBE infra needs to handle when calling other macros with the expansion, and convert to rowan tree etc., which resulted a *massive* hang.
The test (and also `analysis-stats`) used to crash with stack overflow on this macro, because we were dropping some crazily deep rowan tree. Now they work properly. Because I am lazy, and also because I could not find the exact conditions that causes a macro match but with a missing binding, I just copied all macros from tracing. Easy.
