[libcxx] [test] Fix MSVC x64 truncation warnings with 32-bit allocator size_type/difference_type.

test/std/containers/container.adaptors/queue/queue.cons.alloc/ctor_container_alloc.pass.cpp
test/std/containers/container.adaptors/stack/stack.cons.alloc/ctor_container_alloc.pass.cpp
Iterate with C::size_type because that's what operator[] takes.

test/std/containers/sequences/vector/contiguous.pass.cpp
test/std/strings/basic.string/string.require/contiguous.pass.cpp
Add static_cast<typename C::difference_type> because that's what the iterator's operator+ takes.

Fixes D27777.

llvm-svn: 289734