Strings & string_view

Adds a constrained range constructor to string_view.

Deletes construction of basic_string and basic_string_view from nullptr.

Adds basic_string::resize_and_overwrite for writing directly into uninitialized string storage.

Requires span and basic_string_view to be trivially copyable.

Adds an rvalue overload of string::substr() that moves out of the string.

Makes the string_view range constructor explicit.

Adds string_view-based constructors, view() and str(sv) to string streams.

Makes std::to_string for floating point produce std::format-style shortest round-trip output.

Adds bitset constructors from string_view.

Adds operator+ between basic_string and basic_string_view.

Adds basic_string::subview(), returning a string_view slice without allocating.