Use if-constexpr instead of overloading for customization point

Use if-constexpr instead of overloading for customization point

This combines two of the std::ranges::swap.operator() overloads into a
single function template. Using if-constexpr to choose between
implementations should give the compiler less work to do than using
overloading.

	* include/std/concepts (std::ranges::swap): Use a single overload for
	the non-array cases, and switch using if-constexpr.

From-SVN: r277635