Vectorize basic_string::find_last_of

[AlexGuteniev]

🧭 Overview

• Same pcmpestri approach as in find_first_of for 1 or 2 byte element. Did not bother making anything for larger characters.
• The existing find_first_of was a bit copypasta reduced. Still the _first_ and the _last_ don't share the implementation, it would have been very confusing to iterate in different directions in a single loop.
• The new functions have _pos in names to indicate being position based rather than pointer based. They are used in strings only, so pointers would have been extra conversion for no gain. We might add position-based find_first_of or pointer based find_last_of someday, so the naming scheme has provision for this.
• Also the vectorization threshold was tuned (even for 8-bytes character, you'll hate it).
• Test coverage was also expanded to cover the bug of having basic_string<unsigned long long>.

⏱️ Benchmark results

Benchmark	main	this
bm<AlgType::str_member_last, char>/2/3	7.79 ns	5.56 ns
bm<AlgType::str_member_last, char>/7/4	22.1 ns	12.5 ns
bm<AlgType::str_member_last, char>/9/3	23.8 ns	11.2 ns
bm<AlgType::str_member_last, char>/22/5	37.2 ns	11.9 ns
bm<AlgType::str_member_last, char>/58/2	63.3 ns	13.2 ns
bm<AlgType::str_member_last, char>/102/4	54.0 ns	16.3 ns
bm<AlgType::str_member_last, char>/325/1	119 ns	36.8 ns
bm<AlgType::str_member_last, char>/400/50	156 ns	178 ns
bm<AlgType::str_member_last, char>/1011/11	321 ns	100 ns
bm<AlgType::str_member_last, char>/1502/23	605 ns	308 ns
bm<AlgType::str_member_last, char>/3056/7	916 ns	284 ns
bm<AlgType::str_member_last, wchar_t>/2/3	5.82 ns	5.99 ns
bm<AlgType::str_member_last, wchar_t>/7/4	11.0 ns	11.6 ns
bm<AlgType::str_member_last, wchar_t>/9/3	11.2 ns	11.9 ns
bm<AlgType::str_member_last, wchar_t>/22/5	16.1 ns	12.8 ns
bm<AlgType::str_member_last, wchar_t>/58/2	36.9 ns	17.4 ns
bm<AlgType::str_member_last, wchar_t>/102/4	58.5 ns	24.1 ns
bm<AlgType::str_member_last, wchar_t>/325/1	173 ns	63.7 ns
bm<AlgType::str_member_last, wchar_t>/400/50	191 ns	221 ns
bm<AlgType::str_member_last, wchar_t>/1011/11	396 ns	393 ns
bm<AlgType::str_member_last, wchar_t>/1502/23	658 ns	573 ns
bm<AlgType::str_member_last, wchar_t>/3056/7	1285 ns	548 ns
bm<AlgType::str_member_last, wchar_t, L'\x03B1'>/2/3	6.61 ns	5.64 ns
bm<AlgType::str_member_last, wchar_t, L'\x03B1'>/7/4	22.9 ns	22.5 ns
bm<AlgType::str_member_last, wchar_t, L'\x03B1'>/9/3	24.2 ns	12.1 ns
bm<AlgType::str_member_last, wchar_t, L'\x03B1'>/22/5	83.5 ns	13.0 ns
bm<AlgType::str_member_last, wchar_t, L'\x03B1'>/58/2	66.4 ns	17.7 ns
bm<AlgType::str_member_last, wchar_t, L'\x03B1'>/102/4	162 ns	24.6 ns
bm<AlgType::str_member_last, wchar_t, L'\x03B1'>/325/1	213 ns	63.0 ns
bm<AlgType::str_member_last, wchar_t, L'\x03B1'>/400/50	5418 ns	603 ns
bm<AlgType::str_member_last, wchar_t, L'\x03B1'>/1011/11	4257 ns	523 ns
bm<AlgType::str_member_last, wchar_t, L'\x03B1'>/1502/23	9358 ns	1073 ns
bm<AlgType::str_member_last, wchar_t, L'\x03B1'>/3056/7	6275 ns	550 ns

[StephanTLavavej]

Conflict-free merge with toolset update, no clang-format regen needed.