libstdc++: Add operator bool to <charconv> result types (P2497R0)

libstdc++: Add operator bool to <charconv> result types (P2497R0)

C++26 adds these convenience conversions.

libstdc++-v3/ChangeLog:

	* include/bits/version.def (to_chars): Define new value for
	C++26.
	* include/bits/version.h: Regenerate.
	* include/std/charconv (to_chars_result::operator bool): New
	function.
	(from_chars_result::operator bool): New function.
	* testsuite/20_util/to_chars/version.cc: Update expected value.
	* testsuite/20_util/from_chars/result.cc: New test.
	* testsuite/20_util/to_chars/result.cc: New test.