#119632 introduced a code size and performance regression. This was
verified by running the included benchmark against trunk and trunk with
#119632 reverted. Instead of actually reverting that patch, we can
inline `__construct_at_end` into the few places it's used instead,
simplifying the implementation further (by not handling special cases we
never actually encounter).
```
Benchmark Baseline Candidate Difference % Difference
------------------------ ---------- ----------- ------------ --------------
BM_vector_bool_size_ctor 29.91 8.56 -21.35 -71.37
```
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