Currently there is `NtContinue()` test only for `aarch64` so implement it for amd64 aswell.
This implementation is very similar to `aarch64` and it's very basic test.
It doesn't change/test `ContextFlags` so it won't catch https://bugs.winehq.org/show_bug.cgi?id=56050 but that can be implemented later on top of this.
-- v6: ntdll/tests: Implement test_continue() for amd64