libstdc++: Implement missing operator overloads in max_size_type.h

libstdc++: Implement missing operator overloads in max_size_type.h

This implements operator++, operator-- and operator<=> for the
integer-class types defined in max_size_type.h, which I overlooked
when originally implementing the class.

libstdc++-v3/ChangeLog:

	* include/bits/max_size_type.h (__max_size_type::operator _Tp):
	Fix formatting.
	(__max_size_type::operator++): Define.
	(__max_size_type::operator--): Likewise.
	(__max_size_type::operator<=>): Conditionally define (in place
	of the other comparison operators).
	(__max_diff_type::operator _Tp): Fix formatting.
	(__max_diff_type::operator++): Define.
	(__max_diff_type::operator--): Likewise.
	(__max_diff_type::operator<=>): Conditionally define (in place
	of the other comparison operators).
	* testsuite/std/ranges/iota/max_size_type.cc (test01): Test
	these operator overloads.