[re.regex]/3 regex_constants presentation

[jensmaurer]

Each constant takes up two lines. That's ugly.

We could squeeze each on a single line (with comfortable padding) if we used the flag_type alias for regex_constants::syntax_option_type.

Opinions?

[tkoeppe]

I like the idea of compressing the presentation, which is needlessly noisy at the moment.

@jwakely, @AlisdairM, do you think that would be in line with existing practice?

[AlisdairM]

makes sense to me too, but only if applied consistently through the clause, rather than cherry picking the list of constants in the class definition - we don't want to use two ways of saying the same thing.

[jwakely]

Using flag_type might be the least noisy form.

[jensmaurer]

Editorial meeting consensus: Apply flag_type to synopsis. Remove [re.regex.const]. Call out in the editor's report.