Extend valid values of iostream bitmask types

Extend valid values of iostream bitmask types

	PR libstdc++/56158
	* include/bits/ios_base.h (_Ios_Fmtflags, _Ios_Openmode, _Ios_Iostate):
	Define enumerators to ensure all values of type int are valid values
	of the enumeration type.
	* testsuite/27_io/ios_base/types/fmtflags/case_label.cc: Add new cases.
	* testsuite/27_io/ios_base/types/iostate/case_label.cc: Likewise.
	* testsuite/27_io/ios_base/types/openmode/case_label.cc: Likewise.

From-SVN: r230267