`[\W\D]` fails to match alphabetic characters

The (ECMAScript) regular expression `[\W\D]` describes a character class that matches the union of (a) all non-alphanumeric characters and (b) all non-digits. So effectively, should be equivalent to `[\D]` and thus match all non-digits. However, Boost.Regex actually matches only non-alphanumeric characters.

Test case:
```
#include
#include

using namespace boost;

int main()
{
regex re(R"([\W\D])");
std::cout << "matches alphabetic: " << regex_match("a", re) << '\n'
<< "matches digit: " << regex_match("0", re) << '\n'
<< "matches non-alphanumeric: " << regex_match(".", re);

return 0;
}
```
https://godbolt.org/z/jPf79j5nr

This prints:
```
matches alphabetic: 0
matches digit: 0
matches non-alphanumeric: 1
```

But it should print:
```
matches alphabetic: 1
matches digit: 0
matches non-alphanumeric: 1
```

I think the problem lies here:
https://github.com/boostorg/regex/blob/35937503ca4fff3434a3a5f0d76258231eb442cf/include/boost/regex/v5/basic_regex_creator.hpp#L106-L110

The negated character classes are bitwise or'ed, but De Morgan's law says that `(not w) or (not d) = not (w and d)`, so the bit masks should really be bitwise and'ed.

But bitwise and'ing would be problematic as well, because no requirement is placed on traits classes that and'ing the character class bit masks corresponds to the intersection of the character classes. I guess and'ing will probably still work for traits classes provided by Boost.Regex (although I haven't checked that), but it's not guaranteed to do the right thing for user-provided traits classes.

Reproduce the reported behavior with the C++ example or its Godbolt link, then inspect include/boost/regex/v5/basic_regex_creator.hpp around lines 106-110. Trace how negated character classes are combined and review the constraints on user-provided traits classes. Done means the reported expression matches alphabetic and non-alphanumeric characters but not digits without breaking supported traits behavior.

Written by the indexing model from the issue text.