libstdc++: Support braces as arguments for std::erase on inplace_vector [PR121196]

libstdc++: Support braces as arguments for std::erase on inplace_vector [PR121196]

	PR libstdc++/121196

libstdc++-v3/ChangeLog:

	* include/std/inplace_vector (std::erase): Provide default argument
	for _Up parameter.
	* testsuite/23_containers/inplace_vector/erasure.cc: Add test for
	using braces-init-list as arguments to erase_if and use function
	to verify content of inplace_vector

Reviewed-by: Patrick Palka <ppalka@redhat.com>
Signed-off-by: Tomasz Kamiński <tkaminsk@redhat.com>