libstdc++: port tests away from is_trivial

In preparation for the deprecation of is_trivial (P3247R2).
Mostly a mechanical exercise, replacing is_trivial with
is_trivially_copyable and/or is_trivially_default_constructible
depending on the cases.

libstdc++-v3/ChangeLog:

	* testsuite/20_util/specialized_algorithms/uninitialized_copy/102064.cc:
	Port away from is_trivial.
	* testsuite/20_util/specialized_algorithms/uninitialized_copy_n/102064.cc:
	Likewise.
	* testsuite/20_util/specialized_algorithms/uninitialized_default/94540.cc:
	Likewise.
	* testsuite/20_util/specialized_algorithms/uninitialized_default_n/94540.cc:
	Likewise.
	* testsuite/20_util/specialized_algorithms/uninitialized_fill/102064.cc:
	Likewise.
	* testsuite/20_util/specialized_algorithms/uninitialized_fill_n/102064.cc:
	Likewise.
	* testsuite/20_util/specialized_algorithms/uninitialized_value_construct/94540.cc:
	Likewise.
	* testsuite/20_util/specialized_algorithms/uninitialized_value_construct_n/94540.cc:
	Likewise.
	* testsuite/23_containers/vector/cons/94540.cc: Likewise.
	* testsuite/25_algorithms/copy/move_iterators/69478.cc:
	Likewise.
	* testsuite/25_algorithms/copy_backward/move_iterators/69478.cc:
	Likewise.
	* testsuite/25_algorithms/move/69478.cc: Likewise.
	* testsuite/25_algorithms/move_backward/69478.cc: Likewise.
	* testsuite/25_algorithms/rotate/constrained.cc: Likewise.
	* testsuite/25_algorithms/rotate_copy/constrained.cc: Likewise.

Signed-off-by: Giuseppe D'Angelo <giuseppe.dangelo@kdab.com>