Vectorize find_first_not_of/find_last_not_of member functions (single character)

[AlexGuteniev]

Another basic_string vectorization.

🎲 Decisions

Some nearly-arbitrary decisions, can change if needed.

• Return position in "last" but pointer in "first". For "first", pointer has to be adjusted in header due to unknown original beginning and not passing it due to _Start_at applying. For "last", can adjust in the separately compiled code, and can potentially use it for future micro-optimization.
• Specialize for 32 and 64 bit character too. Not very useful, but general algorithm is written already.

⏱️ Benchmark results

Benchmark	main	this
bm<char, not_highly_aligned_allocator, Op::StringFindNotFirstOne>/8021/3056	738 ns	49.8 ns
bm<char, not_highly_aligned_allocator, Op::StringFindNotFirstOne>/63/62	17.9 ns	4.78 ns
bm<char, not_highly_aligned_allocator, Op::StringFindNotFirstOne>/31/30	9.56 ns	5.71 ns
bm<char, not_highly_aligned_allocator, Op::StringFindNotFirstOne>/15/14	4.76 ns	5.34 ns
bm<char, not_highly_aligned_allocator, Op::StringFindNotFirstOne>/7/6	2.77 ns	3.23 ns
bm<char, not_highly_aligned_allocator, Op::StringFindNotLastOne>/8021/3056	740 ns	49.8 ns
bm<char, not_highly_aligned_allocator, Op::StringFindNotLastOne>/63/62	25.7 ns	4.89 ns
bm<char, not_highly_aligned_allocator, Op::StringFindNotLastOne>/31/30	8.88 ns	6.07 ns
bm<char, not_highly_aligned_allocator, Op::StringFindNotLastOne>/15/14	4.72 ns	5.31 ns
bm<char, not_highly_aligned_allocator, Op::StringFindNotLastOne>/7/6	2.51 ns	3.68 ns
bm<wchar_t, not_highly_aligned_allocator, Op::StringFindNotFirstOne>/8021/3056	749 ns	82.8 ns
bm<wchar_t, not_highly_aligned_allocator, Op::StringFindNotFirstOne>/63/62	17.5 ns	4.14 ns
bm<wchar_t, not_highly_aligned_allocator, Op::StringFindNotFirstOne>/31/30	9.58 ns	3.64 ns
bm<wchar_t, not_highly_aligned_allocator, Op::StringFindNotFirstOne>/15/14	7.36 ns	4.65 ns
bm<wchar_t, not_highly_aligned_allocator, Op::StringFindNotFirstOne>/7/6	2.91 ns	4.67 ns
bm<wchar_t, not_highly_aligned_allocator, Op::StringFindNotLastOne>/8021/3056	739 ns	85.1 ns
bm<wchar_t, not_highly_aligned_allocator, Op::StringFindNotLastOne>/63/62	21.5 ns	4.69 ns
bm<wchar_t, not_highly_aligned_allocator, Op::StringFindNotLastOne>/31/30	8.55 ns	4.11 ns
bm<wchar_t, not_highly_aligned_allocator, Op::StringFindNotLastOne>/15/14	4.48 ns	4.38 ns
bm<wchar_t, not_highly_aligned_allocator, Op::StringFindNotLastOne>/7/6	2.40 ns	3.63 ns
bm<char32_t, not_highly_aligned_allocator, Op::StringFindNotFirstOne>/8021/3056	737 ns	157 ns
bm<char32_t, not_highly_aligned_allocator, Op::StringFindNotFirstOne>/63/62	17.4 ns	5.51 ns
bm<char32_t, not_highly_aligned_allocator, Op::StringFindNotFirstOne>/31/30	9.39 ns	4.03 ns
bm<char32_t, not_highly_aligned_allocator, Op::StringFindNotFirstOne>/15/14	6.90 ns	3.39 ns
bm<char32_t, not_highly_aligned_allocator, Op::StringFindNotFirstOne>/7/6	2.95 ns	3.17 ns
bm<char32_t, not_highly_aligned_allocator, Op::StringFindNotLastOne>/8021/3056	737 ns	159 ns
bm<char32_t, not_highly_aligned_allocator, Op::StringFindNotLastOne>/63/62	17.5 ns	6.31 ns
bm<char32_t, not_highly_aligned_allocator, Op::StringFindNotLastOne>/31/30	8.83 ns	4.62 ns
bm<char32_t, not_highly_aligned_allocator, Op::StringFindNotLastOne>/15/14	4.52 ns	4.08 ns
bm<char32_t, not_highly_aligned_allocator, Op::StringFindNotLastOne>/7/6	2.63 ns	3.41 ns