Restructure [utilities]

[jensmaurer]

Ideas from Belfast editorial session:

• Utility types: pair, tuple, variant, optional, any, bitset
• Memory management: memory, smart Pointers, memory resource, scoped_allocator-adaptor,
• Compile-time programming: type_traits, ratio

[jensmaurer]

Move [format] to [strings], since it's essentially a fancy string constructor.

[jensmaurer]

Move [stacktrace] to [diagnostics].

[jensmaurer]

keep Utility types: pair, tuple, variant, optional, any, bitset under [utilities], but create a new grouping subclause called "data types".

[JohelEGP]

Isn't "[charconv] Primitive numeric conversions" a good fit for Clause 26 "Numerics library"? I always searched there for it, at first.

[jwakely]

Should [intseq] "Compile-time integer sequences" be a subclause of [utility] "Utility components" rather than a sibling?

[jensmaurer]

Addressed with #5124