Simplify JLI_Open on Windows in native code (libjli)

This is a follow up to JDK-8217093 which added a CreateFileW after a failing open call to support extended-length paths in parse_manifest.c.

The whole flow of this shall be reevaluated, e.g. checking whether only CreateFileW can be used instead of open. It would also be beneficial to add a testcase for this codepath (and which tests the long paths).