<regex>: Speed up skip optimization for default regex_traits in collate mode

[muellerj2]

In the default std::regex_traits<char> and std::regex_traits<wchar_t> implementation, the translate() function just returns its argument unchanged (see [re.traits]/4). This means that the call to this function can be skipped for these traits classes.

This PR implements this change, and as a consequence, the skip optimization now engages the vectorized std::search implementation in collate mode as well.

The tests added by #5553 already check correct handling of translate() in the skip optimization for user-provided regex traits, so this PR just adds a short variant of this test for default std::regex and std::wregex.

Benchmark (only relevant lines):

name	before	after	speedup
bm_lorem_search/"bibe"/2	2825 ns	2915 ns	0.97
bm_lorem_search/"bibe"/3	5625 ns	5580 ns	1.01
bm_lorem_search/"bibe"/4	10986 ns	11160 ns	0.98
bm_lorem_search/"bibe".collate/2	15346 ns	2915 ns	5.26
bm_lorem_search/"bibe".collate/3	30482 ns	5625 ns	5.42
bm_lorem_search/"bibe".collate/4	61384 ns	11718 ns	5.24

[StephanTLavavej]

I'm mirroring this to the MSVC-internal repo - please notify me if any further changes are pushed.

[StephanTLavavej]

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