[libcxx] Fix the type attribute for a couple templates

Use `_LIBCPP_TEMPLATE_VIS` instead of `_LIBCPP_TYPE_VIS` for a template
class.

This fixes the nodiscard_extensions.pass.cpp and a couple
func.search.default test cases when built in MSVC/DLL configurations.

Differential Revision: https://reviews.llvm.org/D99932