libstdc++: Declutter std::optional and std:variant pretty printers [PR110944]

libstdc++: Declutter std::optional and std:variant pretty printers [PR110944]

As the PR says, including the template arguments in the GDB output of
these class templates can result in very long names, especially for
std::variant. You can use 'whatis' or other GDB commands to get details
of the type, we don't need to include it in the value.

We could consider including the type if it's not too long, but I think
consistency is better (and we already omit the template arguments for
std::vector and other class templates).

libstdc++-v3/ChangeLog:

	PR libstdc++/110944
	* python/libstdcxx/v6/printers.py (StdExpOptionalPrinter): Do
	not show template arguments.
	(StdVariantPrinter): Likewise.
	* testsuite/libstdc++-prettyprinters/compat.cc: Adjust expected
	output.
	* testsuite/libstdc++-prettyprinters/cxx17.cc: Likewise.
	* testsuite/libstdc++-prettyprinters/libfundts.cc: Likewise.